The trouble with Amazon or Ebay is returns. You have a LOT more liability then selling on forums. On forums great thing is most likely person knows how to mine, so no teaching. And I LOVE to teach mining, just not a ton in a row when I'm getting rid of previous gen. Also on forum you get cash without a cut taken out.
If I don't sell for fair price on forum I then go to ebay. And I do keep in mine ebay fee's and paypal add up, they double dip with taking too fee's. The crazy thing is they also take fees out of shipping price on Ebay, as some abused it when it had no fee's. So I have to markup shipping to break even.
On ebay I put up a Buy It Now, that is high for the item. This allows for offers to come in to me and I can pick someone with good feedback. I hate selling to new users.
They do in deed double dip or charge a fee for a fee, same thing to me as double dipping . and there so called discounts they get back in other ways they don't lose a thing after my last S5 sells there not again I couldn't believe some of the uness fees they charged me .
btw the Avalon 4.1's i bought off the forums is mining a way i wish i had bought them back then , i Burt up a breakout board over clocking it to much unless somethng was wrong with that board which i doubt i missed used it by oc to high , those Avalon 4.1's are beasts. saving for a A6 now , i want one just to see how far i can push it.