beware of the products. i bought off geartrade from the seller of backcountry. the description they used for the skis said that they had no edge issues and no problems saying they were only ridden a couple of times. once i got the skis they had 15 edge cracks and 2 pull outs. it turns out they use the description from the person that returned the skis and that person lied. luckily i was able to return the skis to get a full refund. But still be aware that you are buying return skis from backcountry or a private seller
it isn't an auction website, but you can still make offers on things and see if people accept it. So if someone lists something at $70, you can message them and just offer 60 and see if they accept it and sell it to you.
It is a legit way of doing OBO