I may just repost this every month or so. The world of original comic art collecting needs a big, neon CAVEAT EMPTOR sign flashing in the faces of all buyers. There's an awful lot of stuff on the market — and in online auctions, especially — that is either innocently misidentified or deviously forged. Right now over at America's Marketplace (eBay to you), someone is selling a page from the Hulk story in Tales to Astonish #73 (the panel above is from that story) and they say it was penciled by Jack Kirby and inked by Bob Powell.
No, it wasn't. The printed credits on that issue say that Jack did layouts, not pencils. Layouts are substantially less, as evidenced by the fact that Jack received 25% of the rate he'd get if he just drew the page in pencil. Then the published credits say "Art by Bob Powell," suggesting he penciled and inked…and even that's not right because the art was actually roughed out by Kirby, penciled by Powell and inked by Mike Esposito.
This one's an easy, blameless misidentification. Others aren't so innocent. There are a couple of artists whose work is habitually faked…and usually not even that well. Be especially wary of unpublished sketches, especially if they aren't signed to anyone. Charles Schulz never had much of a reason to sit down and do a great finished drawing of Snoopy in a classic pose unless it was a gift to somebody and thus signed to that person. He usually also managed to spell his own last name right.
So be skeptical and remember that just because someone sells original art doesn't mean they have the slightest ability to discern who actually did it. Some have good eyes for this kind of thing but some don't. And the ones in the "don't" category often have very strong motives to believe that a given piece of art is real and that it's by the guy whose work goes for the high price.