QUOTE (SoxFan1 @ Mar 14, 2010 -> 06:27 PM)
Those are all pretty spot on. Another thing to look for is the size/thickness of the font used for the numbers and lettering. If you know the White Sox jerseys well enough, spotting fakes is easy. Often times the lettering will be extremely thick or much thinner than usual.
Another is the spacing of the numbers and letters, as Soxpride said. If they're unusually far apart or stacked right next to each other, its not authentic. Also, if the names are VERY curved around the numbers, it's probably a fake. This happens a lot with Pierzynski jerseys I see on eBay.
Another tell is the patches on the sleeves. The Sox use the diamond Sox logo on their left sleeve on the road greys and alternate blacks.
Lastly, pay attention to the trim around the names and letters. The White Sox jerseys have multi-colored trim. For instance, the alternate black jerseys have white letters with a black outline and a grey trim. The road grey jerseys are black with a white outline, and the home white jerseys have black letters/numbers with grey trim.
If all else fails, just give it the Google test.
Here's an example of a pretty good fake: http://cgi.ebay.com/NEW-Mark-Buehrle-White...8#ht_500wt_1182
You'll notice the shinier fabric, especially on the sleeve patch. It's also a size 50, which doesn't exist. The numbering/letting is pretty damn good, but it's not authentic.
Notice the difference between the numbering on the right chest? The jersey on eBay has much thinner numbering.
The MLB tag is also off on the Ebay jersey. The silver should be on the right side of the batter and the black on the left. Another thing to look for on fakes, as you pointed out, is the Sox patch that is on the left sleeve of away and alternate jerseys. I have seen some pretty crappy fakes with the logo embroidered onto the sleeve.