Just like the other guys said, you have to ask. As long as you don't mention anything about sex, you will be fine.
b-
Some ads, the girls don't have rates listed. Since I assume its taboo to talk about it over the phone, how do I find out how much the rates are?
If the rate isn't listed, then she will most likely mention it when you call. If she doesn't, then you need to ask. You need to discreetly prompt her. I usually start the conversation mentioning the amount of time I would like to visit her for and find out if she is available. Once that has been established then a simple "what is your rate" will suffice.
If she is reviewed (and she should be!) then you can get a ballpark number from the profile. But NEVER trust it because the rates don't get updated.
The first poster gave you some good advice. Only visit ladies that have good reviews, you will save yourself much grief. The lady's price should be listed in her profile. You should be able to ask her about the fee for her time as long as you use discretion.
Just like the other guys said, you have to ask. As long as you don't mention anything about sex, you will be fine.
b-
...and if you don't like using words like 'rate' or 'fee', you can always substitute a lovely euphemism such as donation, roses, kisses, hugs, etc. if that makes it more comfortable for you.
XO,
Stella