Interesting that people have these experiences. I use eBay a lot, mostly buying 2nd hand computer hardware and retro gaming stuff(consoles/games/accessories) and I'd say I have problems with as many as 50% of all my purchases. Some bigger problems where I want to return the item, some smaller ones where I paid extra for postage but it was ignored, that sort of thing. The complaints procedure exist but it's weak(seller sells a "mint condition" genuine PS2 controller, got the controller it's all dirty and with frayed cable, complain to seller, they say "oh it's mint for the age, nothing wrong with it", complain to ebay, seller has a week to respond, nothing, ebay sends me a label to ship it back, have to go to the post office to send it back, wait another week, nothing, ebay finally refunds me my money. You know how it would work with Amazon? I would complain in chat, they would send a courier to pick it up from me the next working day, I would have the money back 5 minutes after the courier picked up the parcel). And then I had someone send me actual expletives-filled email calling me all kinds of worst things in the world because I left a neutral(!!!) feedback on their account, after I paid extra for 1st class postage but they shipped 2nd class. And sellers in general just have no idea about consumer laws(yes, if you sold this item as brand new then you have to accept a 14 day return by law) which leads to arguments and just in general everything being so stressful.

I've had over 200 amazon orders last year, didn't have a problem with a single one of them. Few times I wanted to return something they either sent a courier to collect it from me directly, or just refunded me anyway. And few times I ordered from somewhere else(urrghhh.....Currys) the customer service was absolutely abysmal. I'm just not brave enough to order from anyone but Amazon nowadays*.

*here in the UK, understand the American Amazon is far worse for <reasons>