But perfect to us means nothing when it's under the grading asshole's microscope. "Oh, the lower left corner isn't exactly as sharp as others I've seen, and it's off-center by .5 of a millimeter. It's an 8.5 at best". And now the best Ebay offer you'll get might be several hundred bucks. Ungraded, though, it'd be significantly less than that. The hardcore collectors who are in the market for mint condition cards want graded examples, and the dealers cater to this.
And having dealt with card, coin, comic book and record collectors in the past, I can say with total confidence that sports card dealers are almost invariably gigantic assholes who'll do whatever it takes to rob you blind at any opportunity. "Oh, what's that? A Honus Wagner rookie? Meh. I have twelve of 'em I can't move as it is. I'll give you fifty bucks for it". Coin guys are equally shitty, too.