Wandering Monster/Negotiating Help

[bokenboy]

Me and my friends recently started playing Munchkin. Last week, I was facing a monster I wasn't strong enough to beat. I negotiated with another player for her to help me. After the agreement was made, a third player player used a Wondering Monster card and added a really powerful 2nd monster to the fight (level 20+). The player I made the deal with said she would continue to help me, but demanded all the treasure from the additional monster. Based on all of that, here are my questions:

1) Once you negotiate a deal with a player for assistance, can the terms of the deal be changed after the fact (i.e. could the player offering assistance demand the additional treasure, or does the player have to stick to the original terms of the deal)?

2) With Wondering Monster, do you receive the benefits from beating the additional monster(s) (i.e. additional sets of levels/treasure), or only the benefits from the original monster?

3) Can more than one monster be added using the Wondering Monster card?