These cameras have been rock solid for me in the past and I would perform a basic test on the device before having escrow released. My original Hero 4 from many years ago is still going strong after multiple rain/underwater/snow trips utilizing an extended battery and custom case. If the item I've purchased does not work as my other Hero 4 Black does, I'd expect the seller to cooperate with a basic return. 
I'm not talking about DOA, I'm talking about it failing at a time where you can't ethically ask for recourse or cooperation from a private seller that sold it to you sealed new, and because as far as GoPro is concerned, with no proof of purchase from an authorized retailer, they don't have to honor any warranty.
So, if you want someone to buy that one on Overstock with their BTC, you reimburse them their BTC PLUS the cost of reshipping/inconvenience fee, and want to flush your BTC when it dies after the successful unboxing test & escrow release? Wow.
I don't believe the situation you're describing is accurate and find it odd you're honestly this worried about a possible seller you've lost trust in before the sale has begun.
It's not a matter of trust, it's too-high expectations. If you came back to me and said "That sealed new GoPro I bought from you that I confirmed wasn't DOA & released escrow for, it broke. Help me take advantage of the warranty that is tied to your proof of purchase with your name, your address, your payment info attached." I'd legally be in the clear ignoring your message or even telling you to pound sand, because that's not how warranties are supposed to work. You waive the protection if you didn't, from an authorized retailer, buy it, didn't get a gift receipt, nor buy a third-party warranty like SquareTrade (which requires the original receipt, not a hand-written scrap of paper from the middleman BTCtalker).
I bought my first 2 on ebay from individuals, I don't believe the protections you speak of were available there either.
To conclude: I think you've provided a theoretical scenario for which I'm not really worried and don't care to discuss any further.
