At the NCBC, we have a policy of not allowing trading or selling. When we receive a bike donation, we record the donor's information and the bike's serial #. We have a good relationship with the local PD so that everyone receiving a donated bike also gets the bike registered, right in our shop, before taking it off the premises. We do not, however, check a database of stolen goods when we receive a bicycle donated into our shop - I really appreciate this suggestion (by the way does anyone have a quick link to such a database in the U.S.?).