I've been an Ebay member for 21 years but my experience is mostly with buying! Ebay trading has changed since they dropped PayPal as a default payment method. All payments from buyers like me go to 'eBay Commerce UK Ltd' not directly to the seller, look at your card statements. In the past, sellers would faciltate their own delivery using parcel firms like DPD, DHL, Evri etc. But now sellers moving a lot of items use and pay eBay to be their 'facilitator' to manage the money transfer between buyer & seller and shipping items you bought. It seems similar to Amazon warehousing. A seller stocks a warehouse/storage unit with their items and the orders coming in are fulfilled by a third party who a seller may have less control over?
The tracking systems used by carriers can be exploited by flaws in their system. A tracking number can be generated immediately you checkout, but the item may not actually be in stock and you will see no movement of the item you bought from the first stage of 'Item despatched'. Another trick: If you clicked by mistake at checkout, you have no time to submit an eBay automated cancellation request for a refund after a tracking number has been (automatically?) generated. You have to ask the seller nicely via eBay messaging to cancel your mistaken order which they might refuse, or not reply to your mesage.
When you receive an item, its barcode is scanned as confirmation they delivered it. But it could be scanned and left at the wrong address! eBay uses the tracking delivered confirmation to prove delivery if you raise an item not delivered case. That's why some carriers are now taking a phone photo of the item where it was left and most are 'Drop & run'. We see this many times on our CCTV, no call is made, the item is left and they get away as quick as possible. Even when an item has a tracking label, the delivery company may not scan its barcode but use their mobile phone to a call center to say 'Item delivered'.
IMHO Asian sellers may try to pass off fakes and items 'not as described', but I've always managed to get eBay refunds because the items are usually sent with valid tracking numbers. The problem with some Asian sellers is they use fake returns addresses and UK post codes. I use Google Earth to check a post code address returns location and add my own 'from' address so it comes back to me. When you return an item tracked with an eBay return label, it never gets delivered and may come back to you a week later! eBay returns system has to see their barcode scanned at the seller address before you are refunded. The other trick they use is to send a totally different cheap and insignificant item without enclosing paperwork and you have to be a detective to link it to the real item you bought. I've had more success using eBay for Asian items than Ali, it's harder to get problems sorted and money back with Ali. Also Chinese websites often list many items they do not stock, they are just fishing and will try to source an item after you pay them.
I have used eBay for house and room renovation projects in the past. But it's when you order multiple items needed for a project you see the flaws which now seem to be on the delivery and order fulfilment side? For me, eBay has now become the Wild West of online buying with more loopholes being exploited by the larger companies and a disproportionate amount of my time spent on 'Chat' to raise a case and get it resolved. eBay still works well for private sellers of individual items concerned to get good feedback and keep their reputation.
An interesting issue for U.K consumer law and your rights is where the Contract between you lies when goods are bought online from a seller, but payment is made indirectly to eBay acting as a third party facilitator? I suspect you have no rights until after some (long) time until eBay releases payment to the seller?