I think creating unofficial community rules like this is mostly unenforceable and will just turn people off to this forum.
For example, someone from Boston happens across a great deal in California and posts with the idea of tipping off fellow pinsiders to it. Someone in CA who already knew about it gets all butthurt that the Boston guy "ruined" his stealth buy and jumps on the forum. "Hey boston dummy, didn't you know our "rule" about not spoiling deals?" "That rules is dumb" "You're dumb" "The red sox suck."