How do we know what to expect after we give a provider money? Do we negotiate specifics before handing over any money? Or, do we just need to go on faith that we will get what we want?

This is The Erotic Review! You should start by reading the the self help guide on the main page of the newbie board. Good luck, you'll need it!

First you do your homework. Read the ladies reviews, including the The Juicy Details, this requires VIP. VIP is well worth it. A year of VIP is cheaper than one bad date. Check and read her reviews on other sites as well. Back-channel with those who have seen her if possible. If multiple sources say she offers what you want she likely will if your clean and polite will give you what you want. You will want to check up on those sources and make sure they are on the up and up by checking there review history.

After you do your homework you just have to go on faith. Never negotiate specific sex acts and money in the same conversation. In fact I don't generally talk money at all on my paid dates. I just pay her fee the way she requests I do and all but once was very happy.

find that negotiating rates is frowned upon by providers.  Might just be the quickest way to not get a reply to an e-mail or a quick dialtone if talking on the phone.

...if you attempt to discuss specific sex acts with a provider in an e-mail or phone call you will get cut off immediately.  If you aren't, suspect LE.  The only time you can discuss sex acts with a provider is afte you've arrive, dropped the envelope and disrobed.  That's how she can be sure you're not LE.  Please to read the guide and as much of the Newbie board as you possibly can.  It's all been said before, numerous times.