I imagine the broker is going to Cannes next month.
Well, if the broker is legit and you made the film for $100-$360k that is great, and if you made it for $2M that is not so great. Ask the broker point blank who they are going to sell it to and why they can get access - brokers/agents are often former Studio VP's/suits.
Find out when the lump sum gets paid, whether or not Prints and Advertising gets charged against the sum, what your deliverables are (will have you have to blow up to 35mm?), etc. The broker will probably say "I don't know yet, it depends on the buyer" but at least this will help you hear the thinking processs.
Read "Down and Dirty Pictures" for more insight into the shenanigans surrounding this process..
For humor value allow the broker to earn 10% commission on $400k, but demand that it must be all spent in 3 nights in Monaco.