Nothing wrong with eBay providing one knows where one stands and what the rules of the game are. Unfortunately a lot of people seem to have the impression and perpetuate it that eBay is something it is not, consider it to always be no different to online shopping from a commercial manufacturer or seller.
Try as eBay and other online auctions might, they can never ensure everything being sold is above board, is or works as claimed, is of safe or merchantable quality, or the seller isn't a sink-hole for your PayPal money to go into.
I buy a fair amount of stuff at car boot / garage sales and have some absolute bargains but I have also bought stuff which has only been fit for the bin. I usually don't ask if something works because I've found most people will simply lie if it doesn't, and if they'll do that to your face then they'll have even less hesitation when selling anonymously from a distance. If they are selling something dirt-cheap, claiming it works but doesn't, and it can be fixed then the last laugh is on them, but that's not always the case. Be prepared to have been ripped-off, don't expect any come-back.
With a reputable company, properly constituted, run and controlled by legislation, there are protections against all of those things which eBay and private sellers simply cannot offer. There's no harm in mentioning that, and, particularly as this is a Rev-Ed run and paid for forum, no harm in suggesting or promoting Rev-Ed alternatives.
And, how many eBay sellers offer good customer support and forums ? They often sell cheap by avoiding those overheads, but then purchasers come here and to other forums for that support and help which can end up as taking everyone else for a ride. It's a simple point of principle to support those who strive to do a good job compared to those who simply foist issues off to others.