If this player is in your neighborhood - no worries, it reshuffles every 2 weeks, and you get a new selection of players like this (and possibly a selection that has no players like this). If this player is on your friends list - easy thing, unfriend the player. If the player is in your guild - talk to your guild or find a new guild.
And really - so what if that player gets lucky as a freeloader? How does that bother your game? Worst case scenario - it costs you 1 less FP to level up a building (ergo, there is no loss to you at all - you only gain, even if it is just an immaterial gain). If you have friends to level buildings up with, then this freeloader will not matter. Best thing you can do - is only unlock a new level on a GB when you are ready to use it. Otherwise, leave your GBs locked up.