Most provider rates are all inclusive.  Some will charge extra for things like Greek or some fetish play.  In these cases, tips could be given for exceptional service or if you're trying to make a good impression on a lady you want to see again.  Many people never tip.

I'm guessing that when you say "incall establishment", you're talking about AMPs where you pay a massage fee to get in but have to tip the girl for services.  Few providers work this way.  It's called "upselling".  This is generally thought of as almost as bad as being a rip off.

You can find a lot of guys' opinions on tipping if you do a search.