I would advise against ever buying a used AR from Cabelas unless it is completely factory. The guys in the gun library generally know very little about ARs and mark and sell the gun based on what the seller tells them.
If cabelas buys a custom build, they essentially sell it as if the entire rifle is made by whatever company is marked on the lower. I have seen this personally on several rifles. Have pointed it out to employees and seen the tag and price unchanged when I came back later. Disappointing.
"God made man, but Samuel Colt made them equal."