I used the "wallet in the car trick" when I was greener and less confident about punting. Now if I'm in any doubt before I arrive (eg. if the ad was on VS) I leave their advert open on my phone, and if when the pictures turn out to be a bunch of shite, take the phone out and let them know this is who I was expecting. Thankfully only had to do this twice. And one of those times I stayed anyway...
Otherwise, honesty wins - sorry, I was looking forward to this service / girl / outfit / whatever.