Without being entirely clear on the specifics, if my gut says no then so do I. Unless it's very obviously nerves then a pain in the arse doesn't magically become a nice customer just by uttering one or two words.
I got a harsh reminder of this the other day when I let one slip through who I had my doubts about but told myself I was just tired and let it go. That half hour was like Shit Punter Bingo (got the directions wrong, asked if I was alone in the flat, asked how many bookings I'd done so far today, moaned about the temperature, whinged about having to pay a normal rate for anal, whinged because he couldn't keep it up to come more than once and then told me that when he saw Flossie last week he came seventeen times in half an hour and rounded it off by telling me where Flossies flat is).
So yeah, you get the idea