After driving a supercharged 3800, the average person can definitely make the mistake of claiming it is V8-powered just because of the performance. I rode in a buddy'* Park Avenue Ultra for the first time, and he was raving about the acceleration. I made a comment about how stout the L67 is, and he said something to the effect of, "No way this has a V6! It takes off way too fast!"
I was forced to open his owner'* manual and prove the error of his ways
Still, as Bugsi said, ignorant car salesmen are plentiful. As long as you know what you're looking at, don't pay any mind to off-the-wall claims he might make.