I recently sold my AR and just posted the ammo in gunbroker. Once it sells, what documentation do I need to ask from the seller to make sure I don't have any legal issues?
If it's your own personal ammo, no documentation is needed. You might want to make sure that the buyer is over 18 and lives in a state that can receive ammo from out-of-state. You can ship ammo via UPS Ground and Fedex.
I've sold some ammo on GB before. I always got a copy of the guy's drivers license and a signed written statement from him stating that it is legal for him to buy/own this ammunition where he lives.