This morning I did Hafaros Nedarim, where a panel of 3 people from my shul became 'Dayanim' and were Matir my Nedarim. Considering these were just regular people from my shul, this gave me the question: What's stopping any group of 3 (or more) jews from getting together, and declaring themselves a Beis Din? They can then proceed to rule on monetary matters and declare people's property Hefker, or transfer people's money in to a 3rd party who has agreed to share it with them. If anyone can be part of a Beis Din in shul, why can't they do this in other cases as well?
This question shows opinions on which Beis Din can make things Hefker, and there are opinions that hold even a Beis Din of Hedyotos can make items Hefker!