I had a similar experience, ASavageFox. Last fall I went to a small gun show and a guy had a Model 21- cased and he had a sign saying it was a 12 gauge. I didn't really pay that much attention to the sign, just the $3500.00 he had marked on it. It was a nice gun but was a bit too expensive for the crowd. By the time I was getting ready to leave, he had it marked down to $3200.00 so I bought it. I noticed it was a twenty gauge when I was handling it, but I didn't really put two and two together that he had it marked as a twelve. I realized the mix up when I got home and saw the sign he left inside the case. The gun was a little too small for the case, so he must have thought it really was a 12. Or maybe he really did know it was a 20. I don't know. I have been back twice to the same show but I haven't run across the guy. No one seems to know who he was. He just came in a sat down at one of the tables and pulled out a few guns, I guess. But I sure got a nice 20 gauge SK/SK Model 21- 20 gauge pretty cheap as far as I am concerned. And in an original old Winchester case that is probably for a 12 gauge. Oh well.
