I hear you GP but I think it depends what they are asking.
I have got a few guys who are older and have health issues and they've asked specific questions about their conditions (e.g. nerve damage and have difficulty staying hard, spinal problems so can only fuck in certain positions, etc.) They've said the "if we get on I'd like 2 hours" thing, and I've said to them "Well book 2 hours, and if you don't like me then we'll call it an hour and I'll refund the difference."
The thing is for me, when I'm on tour I need to book guys at regular intervals. If I have someone farting about saying "If we click I'll extend" then I'll just be straight and say "Look, if you want longer then book it, because if I get a definite booking for half hour after you arrive then I'll take it. But if you get here and I don't have another booking, then yes you can extend."
I've also said to guys "Ok why not book half an hour today and if you like me, you can come back again for a longer session another day."
The majority of guys who say "If we click" seem to think they're on a dating site, or they are dangling a carrot in the hopes you'll give them free time, in my experience. The exception is definitely the guys with health problems; to them it's really important to find a provider who will take the time to understand their needs, and I definitely don't mind doing that, i find it really rewarding.