When buying something only first, you need to check that rules and regulations and especially if the website is legit. We all know that sooner amazon and ebay will accept bitcoin as a payment and I think it would be the same as any other online payment or like pay-pal. If you don't receive your package or the product they will refund you on how much it costs. Example, if you buy a bot for 2 BTC they will refund you your 2 BTC and the value of the 2 BTC doesn't matter because that's how bitcoin works its not stable and your taking the risks of using your bitcoin. You would be just very unlucky if you don't get your product.
Yes, there are several stores which already accept Bitcoin as a method of payment. Refund, as you stated, works just like any other payment system. If you don't receive the item, you get the refund. Yet I know there are some stores which don't refund if you pay with Bitcoin.
Regarding Amazon or Ebay acceptance, I think Amazon will come first. Maybe ebay will never come. Don't forget ebay owns Paypal as well, so Bitcoin is a direct competitor they are afraid to accept.