It took three clicks to find the applicable eBay policy statement. It looks like a 9-round magazine and walnut grips were fine, so someone in the vetting department may have gotten overzealous in pulling the auction, which might explain why they're back again.
http://pages.ebay.com/help/policies/firearms.html
Firearms
eBay does not permit the sale of firearms. This prohibition applies to any item designed to propel a metal (or similar) projectile, and includes all sporting, collectible, curio and relic (C&R), antique and "pre-ban" firearms. "Pre-ban" refers to firearms restricted in Title XI, subtitle A of the Violent Crime Control and Law Enforcement Act of 1994. There is no exception to this policy for items that no longer have the capability to fire a shot.
Firearm Parts and Accessories
eBay does not permit the sale of any assault weapon-related parts or accessories. This prohibition applies to all parts and accessories related to any firearm defined as an "assault weapon" by federal or California law.
eBay does not permit the sale of firearm receivers or firearm frames, whether complete receivers and frames, components and parts of receivers and frames, or "cut" or "80%" receivers. eBay also does not permit the sale of any parts or accessories prohibited for sale by federal or California law, including items related to short-barreled shotguns or short-barreled rifles, fully automatic weapons, large-capacity magazines, multi-burst trigger activators and camouflaging firearm containers.
eBay does not permit the following firearms-related items: silencers, converters (items that can be used to give a firearm automatic capability), kits that can be used to create a firearm, flares, flare launchers, flare guns, flare gun receivers, silencers, short barrels ... and any illegal firearm-related items.
eBay permits listings of all other legal gun parts and accessories, including trigger guards, firing pins, barrels, stocks, butt plates, trigger assemblies, pistol grips, holsters and scopes.
BB Guns, Replicas, Blank Guns and Imitation Guns
eBay does not permit the sale of BB guns, air guns, black powder guns or muzzle-loader guns. eBay permits paintball guns, "airsoft" guns, and replica, "look-alike," and imitation firearms under certain circumstances. "Airsoft" guns may only be sold domestically in the United States. The "airsoft" gun must be located in the U.S., offered only for domestic shipment and the seller must be located in the U.S. Replica and imitation items must have clear markings permanently affixed to the items to the extent required by federal law (commonly a blaze orange plug inserted in the barrel), and must not be readily convertible to shoot a projectile. These rules apply even to novelty items designed to look like firearms.
Ammunition and Bullets
eBay does not permit high-capacity magazines (magazines that can hold more than 10 rounds), ammunition with propellant (such as gunpowder) or blank ammunition. eBay permits other non-propellant items used in "reloading bullets" such as brass casings, bullets, and reloading tools. Sellers must state in their listings the actual capacities of any magazines listed.
Militaria, Ordnance and Grenades
eBay does not permit sale of equipment and supplies issued to and formerly used by United States Armed Forces that have not been disposed of in accordance with Department of Defense demilitarization policies. Sales of such items may constitute violations of federal law.
eBay does not permit ordnance (military weaponry, ammunition, and related parts), even if the item is "unserviceable" or has been "demilitarized" or "demilled," as eBay cannot confirm that the item has effectively and permanently altered for lawful and safe transport and sale. However, unserviceable military-type weapons may be listed if the listing contains a clear scan of official documentation from the U.S. Bureau of Alcohol, Tobacco and Firearms (ATF) stating that the item is unserviceable or demilitarized. Contact your local ATF office for more details on obtaining such documentation.
eBay does not permit grenades, including metal military practice grenades, rifle grenades, dummy grenades, grenade launcher attachments, and mines. eBay will allow relics, curios, memorabilias, or display items permanently altered to prevent ready modification for use as a grenade.