I don't think anyone sane would buy a two year old android, that would probably push you back to 5.1 for most phones.
I bought an LG G3 for $80. It's running Android 7 and still getting security updates. It will probably be a couple years before it is out of date.
Yep, i sold an iPhone 6 plus 16gb for $550 yesterday. I couldn't believe it. It was just the asking price to start the haggle. Try get more than $50 for a 3 year old samsung.
Where did you sell it?
That is actually incredible. I won't get more than 275GBP for my 128GB!