I’ve not tipped a girl on a failed negotiation…I HAVE and you SHOULD, however, tip a girl that gave you a tour of the joint if it’s your first time getting a tour…OR…if she’s showing you new amenities since the last time you were on property. Tour gets tip.
So far as the premature thing….
I’ve never heard of girls doing this, but I don’t see why they wouldn’t if it was truly an issue for you. Another option: Two-cum-party….or a girl that books by time and not activity. That way you can just give it another go if you go to quick.