Sure, be leery of the guy, but NOT because he was mistaken (like I said earlier...), but because he presented uneducated assumption as fact. There's absolutely nothing wrong with simply saying "I don't know", or "I think" as opposed to "definitely" especially when he has "never seen one before". However, in areas other than varieties, he may be perfectly knowledgeable and a trustworthy dealer, so don't turn a molehill into a mountain based upon this one experience.
Ok, I won't. I do expect some conflict to some degree because like you said, he is just a dealer, not a professional. Thank you for your advice.