Anything and everything probably, it can be seen even in reviews. I was looking up some gloves and often the reviews are split 50/50 between great and complete garbage. I assume that the unlucky half got counterfeits. Recently I have bought some plastic plates to put under a flower pot. The dimensions were completely wrong: as in, the advertised plate was for a pot of 22 cm in diameter and this was even printed twice on the plate itself - it was not even 18cm large. This was on a product with over 4.5 star average.

I still buy stuff on amazon because returns are very simple, but I got into habit of immediately returning anything which is not good enough. I feel that most of the stuff one can buy there is garbage.

Everything! I mean everything! There's fakes of literally everything. Including items you wouldn't think would be profitable to fake.

Books, CD, electronics, baby products, stationary, personal care products including condoms, toys,...

Take a look at this cup. Would you know if Amazon sent you a fake if it's your only Yeti cup? http://www.wideopenspaces.com/fake-yeti-ramblers-on-the-rise...

Many/Most of the time it's going to be difficult to tell unless you have the real version already and do side by side comparison.