As discussed, there is a risk factor. Ive gotten better at identifying UNC, Choice UNC and GEM unc bills on ebay, but still hit and miss. If the seller is reputable, they should be ok with me returning their bills if they are not as described. Important for sellers to take good quality pictures, but even then, you will only know for sure when you have your bill in hand.
I just bought a lot of 9x 1974 $2 bills from a reputable seller, that were supposedly UNC as per his description. The pictures were taken within the money holder, so I knew I was taking a calculated risk. Having dealt with this seller multiple times and with the prices too good to pass on....I took the risk. Unfortunately, they were all pressed and none of them UNC. I gave the seller an option, I return them or he gives them to me at face value. He chose the latter and apologized, mentioning he truly thought they were UNC (which I believe). Again a reputable seller and now I have Christmas gifts to give. Merry Christmas.
As mentioned, there's a few of us here that sell our extras on this site.
Enjoy the risks, losses and rewards, it's all part of the hobby.