I decided to post some tips on playing Rack without using the Free Play mode (where everything is unlocked and you have a bunch of everything). The last one was on tips for research (which is a big aspect of the game): https://www.furaffinity.net/journal/10000391/
While research is a very obvious thing in the game, lab reputation is a somewhat more hidden mechanic of the game. Essentially, if you please your research subjects, the lab reputation goes up. Do a bad job, and the reputation goes down. While this isn't exactly visible in the game, its effects are certainly visible with respect to research subjects willing to pay you.
When you start the game, you'll typically see prices of about 100 or so Fekles. Getting the maximum certainly doesn't hurt in the early stages of the game, but you aren't exactly buying everything in the game with that kind of pay. Additionally, paying subjects may only appear one at a time which reduces your chances of forming strategies.
The thing with reputation is that you can bump this up with either paying subjects or volunteers. Both will have major objectives to complete, but one will pay you Fekles while the other pays you in bonus chemicals. In the earliest stages of the game, both do go a long way in allowing you to afford upgrades.
A great reputation can really make things more affordable. While playing, the highest paying subject I had offered 449 Fekles. I don't know if there is a cap, but it looks like the reputation bumps up the average of what subjects are willing to pay you.
So, what do you do to please clients? The biggest factor is completing the designated objectives for that subject (often referring to the subject name).
Objectives: Some objectives are easier to complete than others. For instance, giving a subject a clit orgasm using your hand is something you can achieve in short order. Other times, it's just edging a subject for a certain period of time. These are relatively straight forward, but other objectives require more thought.
Maximally Submissive: One objective is to make a subject maximally submissive. No matter how angry or dominant a subject is, you can have them bordering on your pleasure slave with the right techniques in this game. First, find something that the subject enjoys that gives them an orgasm. If hand jobs do it, use this to your advantage. You first want to bump up the friendliness a bit with the entice commands. Of commenting on the activity doesn't do it, try the attractiveness. If there's no dice on attractiveness, then try experience. Usually, you can get this up by either one of the first two.
If your client is more angry, this is something you want to get down first. Use the calm nerves command to get this down. This spends your friendliness, so you may need to bump up the friendlieness back up again if one round isn't enough. The goal is to get the indicator to something close like the middle. Doing this first will generally permit you to use more commands later.
The next thing to focus on is your main objective: submissiveness. If the subject is more dominant, you generally want to start this process slow. Have the subject edged up to near orgasm. Then, use the cum command. Once acknowledged, put them over the edge. Once their climax is finished, use the encourage obedience command to double up on your efforts to push them to being more submissive. Most of the time, at this stage, this will work to start bringing down their domination into submissiveness. Lather, rinse, repeat until they are no longer dominant.
Once the subject begins to lean towards the submissive, you might want to use the "use proper title". Sometimes, this doesn't work, but most of the time, they will start being more submissive with this command. Every time they say something, there is a good change that they will use their proper title. Remember to double the effect with the encourage submissiveness command.
To make them talk more, also be sure to use an effective entice command. They will use the proper title more often, speeding up the process of submissiveness.
You don't necessarily have to reprimand every time they forget, but sometimes, this will aid in the submissiveness process.
In the later part of the submissiveness process, try using the beg command. If they are submissive and a bit intimidated, they will obey and beg. Throwing this in every so often will help the process along. After that, you can simply entice, encourage obedience, and command your way to a successful completion of this objective. It's a time consuming process to complete this objective, but it generally works most of the time.
Pain Objectives: This can include biting, or pain for a period of time. You have three tools at your disposal: mouth (biting), electrostimulation electrocution, and slapping. A lot of the time, you'll want to complete this objective first if you draw this one unless you have a very easy objective right off the bat. Complete that one to build on the subjects friendliness because it might go down once attempting to complete this objective.
Slapping seems to be the riskiest of the three as it's easy to give the subject excessive pain (sometimes causing them to quit).
The easiest to access is biting. Generally, try to stick with manual control for this. Start with a harmless suck command (manual) and move the mouse up a bit. This will (most of the time) cause you to start with the open mouth position. From there, use the 3 (or 2 depending on the interaction) and gently click and drag the mouse down. (in the circumstance that this doesn't work and you start with a closed mouth, then it's the opposite starting position) Do this so the subject will feel some pain. You can get a few more nibbles in in a row with this method before the subject asks you to stop.
Between rounds of pain, offer the more pleasant stimulation that the subject enjoys. You'll want to switch between pleasure and brief moments of pain until the objective is complete.
Bite count objectives are generally easier than timed pain objectives because it's less time consuming, but you'll eventually get there. After that, build up that friendliness.
Objectives Subjects Don't Like: These can often be annoying to complete. If you get an objective that, say, gets you to stimulate a subject with a toy, but the subject doesn't like toys, then you'll probably have to work around this to safely complete this objective.
Usually, the objective requires a climax with that specific method. This is easier to complete. Simply find another stimulation method that the subject enjoys and get them close to climax. Before they climax, switch to the toy or two needed to complete the objective. With any luck, you'll be able to cause them to climax before they can complain, allowing you to remove them quickly after.
The more difficult version is requiring them to experience the full arousal. This is rare, but it does happen. To work around this, maximize their friendliness. Do whatever it takes to make them as happy as possible. Then, work up their arousal (i.e. kissing) to get them started up. When they are ready to start building up anticipation, switch to the toy and get them to climax as quickly as possible. From there, you are just crossing your fingers and hoping they don't rage quit in the process.
Friendliness: While completing all three objectives is a big factor in ensuring subject satisfaction, it isn't the only one. You'll also want to build up that friendliness meter up to 100% as well. Use entice and compliments to get there. It will help you a lot.
Climax Count: This seems to be a more subtle factor in getting a positive review. Even with all objectives completed and maximum friendliness, you might still get a mediocre review if you let the subject climax only once. As a general rule, I found that 5 climaxes usually negates this affect.
Climax Quality: Another minor factor seems to be the quality of climaxes. Great and amazing climaxes can help you get that positive review, so get as many of them as possible. One or two bad or ruined climaxes won't end your effort, but you'll ideally want to add a climax or two to make up the difference.
If you have a paying subject give you about 85% or higher, this will help increase the labs reputation. On average, the payouts for subjects will, on average, increase. This will make it easier to afford more expensive equipment.
Be Male: Over time, I've noticed that subjects tend to favor males. So, if you are going for completing the games content legitimately and more easily, be a male scientist. After messing with some settings, I could never shake the game favoring male/male interactions. On occasion, I'll draw a subject that prefers female, but this is extremely rare (often, female scientists are favored as a latent or secret interest instead of a regular interest). If you like a challenge, though, be a female scientist and see if you can build up your lab without changing genders.
I'll go over purchasing strategies next as this is somewhat related to lab reputation.