Wow, what will they think of next! Thanks for the information @Jack D. Young. Keep them coming, the more we know the more we are likely not to make a mistake.
I work for the post office and sell them. Would you be suspicious if someone offered you a roll of hundred-dollar bills for $29 a piece? Stamps are like money and not discounted. The fakes have been documented but I am not going to get into the "tells" in a public forum like this, just think of the $100 bills... It is really sad to see this forum showing fake ads like Face Book...
It might be the selling price. Good Morning Jack, you beat me to it. These fakes have been reported in the Stamp Collecting Press.
These are on just about every media place. Facebook, Listia and Etsy are all selling these. I can tell you a couple of things about them besides the selling price, the gum is terrible and does not stick well. I ordered a small quantity to see what was going on and found this out just to try and discern the differences. Up really close under magnification the inking is also suspect. They are also not tagged for the machines to pick up on.
I'm amazed that people selling these are not quickly arrested. Like you said, it's the same as counterfeiting money.
If enough people foul up the Postal service trying to use these then it just may prompt the fed to finally do something about all these overseas counterfeiters.
It's easy enough to understand why stamps with a stated value sell for less than their face value. They are a pain to use, especially for trivial amounts like 3 cents. Discount postage has been around for many years. Still there is no reason to sell discounted forever stamps. Like the name says, they are always good no matter what the current postage rates are. I know that the post office does sell some stamps for less than face value to distributors, but the discount is very low.