Count de Monet!!! De MO NAY!!!!
Jesus Fucking Christ!
COUNT THE MONEY!!!!
If you think that you're going to protect yourself from the police by using an envelope, you're out of your fucking mind. "Your honor, I had no idea there was money in the envelope." Yeah, that's really going to convince a judge or jury.
The lady is a hooker. The guy is a whoremonger. He's not going to think any less of you if you check the money. If you don't bother to check it, you're agreeing that it's correct.
Most of us HONEST guys will prefer it if you count it right in front of us. I don't want some gal claiming later that I shorted her when I didn't. I don't want some gal discovering that I DID accidentally short her later. I'll always wonder if the lady is lying. She'll always think that I did try to short her deliberately.
If the guy accidentally shorts you and you find it out later, he's always going to think you're scamming him, even if he pays.
Imagine you're driving away from the local grocery store. You get a phone call. "This is Joe at Kroger. After you gave me the cash, and I counted it, decided it was OK, and gave you a receipt, I checked it again, and it wasn't right. Can you come back in and give me the rest?" Yeah, right.
You might get a TINY bit of legal protection if you collect the money after the session, but that's not much protection.