How is auctionarms.com legal?

www.auctionarms.com buys and sells guns in an ebay fashion. I am an avid supporter of the second amendment but question the legality (since I live in illinois and have to adhere to strict gun laws) So, is this website legal? I know different states have different gun laws so then is this legal in all 50 states.

Also, if this is legal and there seems to be a quite large market for guns on the internet, why hasn’t ebay adopted letting their users buy and sell guns?

I’m not familiar with auction arms but presume it works similarly to gunbroker.com which does ebay style auctions, a service I have used. Bottom line is the service only facilitates finding a buyer for the best price. The transaction must take place according to state and more important federal law which prohibits interstate transfers by non-licensees. In the case where I sold a handgun I had the buyer contact a dealer in his area who was willing to recieve the weapon. The dealer sent me a copy of his federal firearms licenses, signed in ink. I took this to UPS which allowed me to legally ship it to the dealer. The dealer then recieves the gun into his inventory as if he had gotten it from a distributor then transfers it on a form 4473 to the buyer for a nominal fee.

Oh, black powder arms which do not use cartridges are except from federal law as are antiques made before 1899 IIRC. Several specific guns have been designated as Curios & Relics* by the BATFE and may be purchased mail order by collectors with the appropriate C&R license.