Let me say at the outset that the largest part of my experience is with spas, studios and massage places (including by girls working independently). However, I suspect that the variations in practice in regard to fees, tips and acceptance of gifts would also apply to all forms of service providers.
I have experienced over the years a fair amount of lowering of prices (fees, tips, offered cash gifts) by girls where a relationship or something beyond the normal provider/customer situation has developed. It doesn't always work out that way. But here's some of what has happened to me (and my wallet).
1. A girl who charged for everything--even for specific extras. But we also went out a lot and took some trips "for free". Finally, after about five years, there were no more charges. That took so long--and during that time she charged for virtually every "extra", so that I put her into the category of "full chargers".
2. A girl who was a co-owner of a shop. So as soon as things got romantic, she refused all tips, and she would only charge half the door fee (for the other owner). So I put her in the category of "low chargers".
3. A girl who was just an employee and charged standard fees and tips (but never for any extra service). However, we spent many hours with each other outside the shop, almost daily, and all "for free". I put her in the category of "normal chargers," but we did develop a real boyfriend-girlfriend relationship, and I never felt that money was a large part of that.
4. A girl who would accept only the door fee plus standard tip (but not for any particular extra services), but gave extraordinary service and saw me every time I visited her city--if I were there two days, I would see her twice each day, and so four times in two days; yet she turned down completely a very large monetary gift offered with no strings attached (in fact, I was leaving for at least six months). So I put her in the category of "low chargers"--normal, but low in relation to what I tried to give her.
5. A girl who would charge the normal fee and tip (but never an added tip for FS or any other extra); however (as soon I became a customer she particularly liked to see) she started charging for only about 2/3 of the time that I was with her. She never said anything about this, but it happened every time. So I put her in the category of "low chargers".
6. A girl who sees me exclusively but is saving for her future. So she charges me for normal fees and tips, plus an additional monthly amount, but not for outside activities--maybe a couple of restaurants each month. So I put her in the category of "full chargers".
To me, a "full charger" is a girl who charges for everything she can get, to have as much money as possible from the time we spend together--even though occasionally we do things on the outside "for free". I think that people in this relationship can genuinely like each other, but there is usually a mutual recognition that without the monetary aspect, the parties would go their separate ways.
A "normal charger" expects the customary fees and tips (but not added tips for added services), but spends enough outside, uncompensated time so that I don't feel that our relationship is primarily or even partly for the money--she could make the same money seeing other people and has all the business she wants. Rather, she needs some funds for school and family, and beyond that she doesn't expect anything.
A "low charger" is someone who gives up fee and tip income or large gifts, as (I suspect) her way of making clear that she cares about me or her way of considering that what we are doing is romantic or special in some way.
None of this necessarily relates to a boyfriend/girlfriend or sugar daddy relationship. I think every relationship is different--and in many cases there really is no relationship beyond that of regular provider and good customer.
I frequently see the fees and tips for some of these girls posted by reviewers on the boards at a level that is considerably more than I pay for the same girl. In those cases, I think the reasons relate to the types of things mentioned in this post.