Also a flag type 2 might gain more support since there is no proof of a written contract violation. But that's up to you really.
I am not sure but I think one can not create two flag against same user in 6 months or something. I have not checked the Turst topic for long time but I can recall that I have seen something about not allowing to create multiple flag against same user by a same accuser.
Regarding the amount, I think the following line will be very appropriate:
Amount Scammed: 0.373 BTC
Total amount in question: 0.373 BTC
Wants to offer: x
Amount want to scam: 0.373 BTC - x
I really did not think this amount thing was too hard to figure LOL