First, I wonder if his account of things is truly factual:  "On the phone we agreed to 1 hour for 140 with multiples. When I got to the room I didn't think I would be up for 2 so I asked if we could just do the 1/2 hour for 80".

Most providers would see this as being played.  First, 80 is a ridiculous fee even for a 1/2 hour and was an insult.  And to spring this on her at the last minute was taking advantage of the situation.  And most guys are going to check their pockets when getting dressed so I am not buying his story either.