I sell alot on ebay. You will get flagged if you mention anything classified by the state of california as an "assault weapon". For instance you could list a single point sling that "fits modern sporting rifles" but can't specifically list something that fits "AR-15, AK-47, FAL, Pistol Caliber Carbine" etc. etc. Even if it's a general part.
True some sellers seem to get away with this, but not forever. There's a team somewhere looking at new listings to see if they violate policy. Eventually a violation will get picked up and removed.
Free float handguards may be classified as a "Barrel Shroud" so that terminology might also be a non-no.