LT, ST, and from ST to LT
Hm, maybe I've been just lucky with my rather naive approach, but usually I always agree on ST first and then extend to LT if performance and chemistry ok. Provided I take her to my hotel and not to an ST place.
Never had a problem with that kind of "on-board upgrade." Ok, the LT upgrade premium after ST might give away a bit too much information if the girl actually likes me or not, being a bit too high in the latter case. Generally, I get quotes from LT=ST price plus "up to you" to double the ST price. Some reject the offer altogether of course (want to have more than one additional customer that night, party with friends with my money, tired of f*ing already.).