Nonsense! Of course, you should try to determine if the seller is a good one or not, but you don't have to know him, lol. Go to winecommune.com or winebid.com and tell those people they're foolish. You'll be the one walking away feeling rather foolish for uttering such sweeping flapdoodle.
Can I tell when a wine is corked, or cooked? You betcha. Sheesh!
I've got a case of '82 Lafite for sale. Would you like to make a bid?