I really understand the concerns about selling the S7 on ebay. The buyer's protection is easily abusable, even if the item is marked as no returns, if a buyer with ill intents buy the miner, they can buy it, mine with it for a while and then file a item not as described and return the miner to get a refund.
Even though they may simply be a very small vocal minority, its probably a good thing to keep in mind. Not sure if there is a way around that but some users reported this.
Basically without having some sort of "as is" agreement, the seller would take all the risks since the buyer can decide to abuse the system to return the miner if the miner drop in value.
Actually selling with a reasonable return policy (14 days is minimum, soon to be increased to 30 days) is better than "no returns". Yes, you have the 14 or 30 day risk, but outside of that you have a chance that eBay seller protection will work. With a "no return" policy you are almost guaranteed to lose the dispute if buyer claims "not as described" and I think that goes up to 45 days.
I've had mixed success with eBay, got a few of miners returned but overall I think it's not that bad. Never sold anything above $1000 though.