Net54baseball.com Forums - 1961 Fleer All Time Greats Fakes

I have recently joined this group. I came across the group when I was looking for information about fake cards. I am primarily a collector but sell a few cards from time to time to help support my collecting costs. I recently sold a 1961 Fleer All Time Greats - George Sisler card. The buyer claimed that it was a fake because he could hold it up too the flashlight on his cell phone and the light would shine through the card. I discovered that this was a test suggested on several other sites. I have checked several of my own 1961 Fleer card and found that in some cases light does not pass through. In other cases, minimal light passes through and in other cases light easily passes through. My question is whether this test definitively identifies fakes and if so how much light must pass through? Is there a substantial number of fakes for the 1961 Fleer set?