Gun Broker or Auction Arms- similar systems- they are the broker only- they never possess any gun, and the deal is between you and the buyer.
You register with each, need a credit card. Each gets a small percentage of the sale price. Gun can only be for sale on ONE site.
If you are selling a modern gun (not antique, not muzzle loader) AFTER you get payment, you ship gun. You do not need a FFL to ship, but it needs to go TO a FFL (if crossing a state line- and a good idea anyway) Buyer sends you FFL name, lic # and address. You can verify that thru the ATF EZ Check system.
The BUYER pays shipping (state how much in the auction) and they pay FFL fee on THEIR end.
Shipping- a private citizen can MAIL a rifle or shotgun with the US Postal Service. You cannot MAIL a handgun. (Chapter 14, Domestic Mail Manual- trust me on this one) DO NOT MAIL AMMO EVER.
You can SHIP a rifle, shotgun, or handgun by UPS or FedEx. NOT from the UPS store down the street- from a hub. HANDGUNS must be shipped Next Day Air- about $70. A cheaper way to send a handgun IS to go to a Dealer, and PAY the dealer to MAIL it to another Dealer. Flat rate Priority box. You pay YOUR dealer.
Tips for auction- good description, good pictures- in focus, well lighted. Look at some of the other pictures- good and bad. Many buyers do not even search "Reserve" auctions- set the starting price as the bottom $$$ you would take, let it go from there. When you get paid, ship promptly.
Spell check yourself. I paid half of what a rifle SHOULD have sold for, since the seller listed it as a MOOSEBURG instead of MOSSBERG. I see M1 Grands, Endfields, K98 Mousers, Smith & Westerns, and Clots.
INSURE the shipment. If you sell to me, and it gets lost in transit, YOU owe me my money back. Insurance is for YOUR benefit. PACK it well- have rec'd guns with barrels poking out of boxes.