I will bet you 100 Bitcoins that Matthew will fulfill his end of the deal within 3 weeks after a conclusion.

This means that if Matthew wins (pirate pays out) Matthew is done and I get 100 Bitcoins from you.
If it is decided that Matthew loses and has to pay you Ƀ250, and he /doesn't/ do so within 3 weeks, I will give you 100 Bitcoins. (The 3 weeks start after it's been decided that Matthew loses. Suggestions on how this should be decided?)

We can use a two-sided escrow on this bet if you want to. I've got a decent rating though.