Always always ask questions about duo partner's
Confirm services and price 3 times
Read everything on your profile and quiz you on it (your profile says you have brown hair but its black/ are you really a student/your profile says you love pink but your bed is blue)
Stare intensely when you undress and ask about every mole/scar/birthmark and try to assess if you are indeed the dress size you claim to be ( caught one reading label in my underwear once)
Any signs of this at the booking stage and I avoid, just because the booking is rarely pleasant, you cant relax and you know every word, move is being scrutinised.