I'm not saying you are one of them Matty, but a lot of guys who want to make sure they can cum more than once in the time they book can't actually physically do it. This for me, is a tad annoying, as I'll go with it the first time and not hold back (which is what I normally have to do) and then once they have cum, they decide that there isn't a chance of a second round.
I am getting to the point where I haven't a clue what the right thing to do is, because I don't like short bookings, (as in 10/15 mins) which is why I don't offer them, but if a guy cums quick and then can't cum again it's all over.
I guess it is easy money, but I'd rather have the full 30 mins and have a bit of mutual fun.