As a disclaimer, I don't consider myself a mean GM that plans on taking away every good reward given to my players. I love the prizes system of fantasy craft, having always hated the christmas trees in 'that other game'.
But, that being said, i imagine with my playinig style, that prizes may be swapping in and out alot during levels, and I was looking more in story reasons as to why certain prizes (particularly magic items) might be removed from the players, if only temporary. Things to keep in mind I though of were taking away some prizes and not others, and limiting it to just loss of prize, and not an adventure or combat.
So, to the forums, just give a post with a plausible explination as to why a prize of any time would be removed from a player (either with or without their 'character consent', as well if it would be temporary or permanently.
1. Collectors from (Insert Organization Name) have targeted the player upon discover that they have an item that is too dangerous to be held by them