I see in a bunch of reviews, at the end, the reviewer writes "treat her right guys"...

I wish that TER would edit it out, it gets annoying to keep seeing it over and over.

Ok cool, thanks. I didn't know if that meant tipping or some special sex act or who knows what..so many people say it.

be nice to her. He liked her very much and wouldn't want a jerk to try to see her, basically.

... we hobbyists are guilty of it sometimes too.  
Don't read too much into anything written on this site. It's all fictitious anyway

I'm not sure if using the line in the review (and I have used it myself) works well to suggest those looking for a different type of interaction take it as a "Must see so I can really fuck her and make her time miserable" or if they take it as a "Off the list, I'll just get BLed from the girl/agency, a bad rep on the provider board and so might have problems down the road".

I probably wrote that too.
I agree it's weird. As if we would say "treat her badly"

She started it.

At first I assumed it was because providers are always going in and out of the business. If you enjoy a particular lady, you hope she doesn't get jaded and retire before you're done with her. So you admonish fellow clients not to do anything that'll drive her away.  

Just means don't be an asshole to her.  If you've been in this game long enough then you've more than likely ran into the jaded provider who 1) Seems to have a lot of "bad days."  2) The provider who always seems to have an attitude or GPS (Golden P**** Syndrome) or 3) Just a really negative attitude during the session.  Most certainly contributed to asshole clients.  All due to guys not "treating her right."  All in all it's just a request from good clients to idiots out there posing as clients don't ruin her attitude toward providing good service.

but the thing we're not talking about here is how this also implies that if a review doesn't say treat her right then that means we're free to mistreat her, which is an odd thing

...my first review was mediocre. The reviewer gave me 5s. He didn't sat anything bad, but nothing great. He claimed he felt there was no connection, and I wasn't into it. Well, he wasn't the nicest guy and had a bit of an attitude. Like he was doing me a favor by being there. Had he approached me more respectfully, and was more active during his session, of course his experience would've been better. Clearly, YMMV...which is why I believe my 2nd reviewer gave me a much better review, stating that if you "treat her right", she's great, etc..and every review since then has been great. It just makes the first one look like an asshole, who I clearly didn't like, based on how he treated me.

I don't know what it means.  I just try to treat people the way that I want to be treated.  And I always do my best to never make people feel uncomfortable -- and feel good about themselves.