I've offered to cut the booking short (incall only) and make it half hour for similar reasons as helen, also a few times I've given money back when I've not particularly enjoyed the client and want them to leave after half an hour or less, ?30 back out of ?100. I've never given money back on an outcall as my minimum booking is one hour for those and if they've booked longer then its their own fault for booking that length of time when I could have been doing other things.
I had a client last week who stated he wanted an hour, long story short he was an annoying twat, he wanted a bath with me, not a problem until he said he wanted me to 'wash his arse for him' then when he got out was acting like a complete idiot, kept trying to push his bum in my face saying "you gonna give me a good rimming" I politely told him I don't do that then suddenly he can't get hard and was pacing the room virtually tantrumming blaming me for his lack of erection! I wanked him off and soon as he came he said "I'm gonna get off now I'm stressed" So I said well you need to pay me, he asked how much so I said its ?100 for the hour, then he had the cheek to say "what even though I haven't been here the full hour?" it had been about 40 mins and I had enough of him by then I was starting to get agitated so I said just make it ?80 then, I was thinking just get the fuck out of my face, he said that's what he was gonna say, wanker!!! He's now in my phone as 'Wanker don't ever see' .