We like to think every one is honest and forthright and many are , but not all. Those selling a shotgun with thin barrel walls even in the forward 1/3 of the barrel might round up the number to .020 ". Is it really .018 .016 .015 " ? Seller hopes that buyer doesn’t have a wall gage. Ask the dealer if he'll make the sale contingent on an independent thickness check and with full return to include shipping both ways if not as advertised.