The 1994 US law that implemented a
"Federal Assault Weapons Ban" gave it a try. By that legal definition the wooden stocked M1 Carbine would not be considered an assault weapon. By that definition, the firearm had to have two cosmetic features:
Semi-automatic
rifles able to accept detachable magazines and two or more of the following:
The M1 Carbine only has one of these cosmetic features, the bayonet mount.
The M1A Carbine (para-trooper model) did conform to the definition, because it had a folding stock and bayonet mount. Thus the magazine that fits either firearm could be associated with an "assault weapon", and Ebay's position conforms to their rules.
Interestingly, the M1 Garand battle rifle did not conform to the definition because it did not have a detachable magazine. It used an enblock clip internal to the receiver.
The 1994 law has expired. Whether that legal definition still stands would be an issue for the courts.
This US law was completely irrational, and accomplished nothing except to interfere with law abiding citizens and their constitutional rights. We have other irrational laws; some of them quite old. For example, Noise suppression of firearms is controlled under the same laws that define and control fully automatic firearms. A very expensive transfer tax and extensive background checks are involved in purchase. In Norway (a more rational approach) encourages the use of noise suppressors to avoid disturbing neighbors when you're hunting and practicing target shooting.
In the popular press in the USA, anything that looks "evil" and shoots is called an "assault weapon". For that reason, the common person unfamiliar with firearms and vulnerable to emotional manipulation by the press thinks of most firearms as "assault weapons". I expect that many would consider Lugers to be "assault weapons".
Marc