I think the main reason we don't allow the sale of DB's is because in the past we've had members trying to sell stolen one's. Even going as far as downloading a DB from scriptmafia saying it's there's and being too stupid to change screenshots from the post on scriptmafia.

Just look below this thread at similar threads you'll see a thread by Luke selling a bunch of hacked DB's.
http://www.besthostingforums.com/11-...-database.html

After that the rule's about DB's started and have stuck since.