It's real simple, either people stand behind what they sell or don't sell it here. That means if there are any problems at all, you make it right or take it back and return the money.
Since this is not getting any attention from the admins or pfs mods, looks like this thread will be in vain.
I think the problem would be trying to enforce anything. You wouldn't believe a lot of stuff I have seen over the years that guys have done with NEW parts Never mind used stuff.