Nice article, Steve!
eBay offers "eBay Money Back Guarantee". Amazon offers a slightly more complicated "A to Z Guarantee" to cover 3rd party sales. Amazon also has a 'Renewed' store which includes 3rd party vendors which might deliver a more comprehensive support if there is a product issue. Depending on which you prefer, it is essential that you read and fully understand whatever warranties or guarantees are offered.
Best advice - do not buy any off-brand or generic items (too many of these are fakes), be aware of from where the item ships, store screenshots/hardcopies in a folder and keep packaging until you are fully satisfied. If bidding, set your maximum price beforehand (I write it on a printout of the item details) and stick to it.
Another bargain will be available tomorrow.