Samsung Repair not that bad
The fact Samsung has its own repair centre's is actually a selling point for me. It's the only flagship phone manufacturer that provides genuine replacement batteries at a reasonable price. If you buy a 2nd hand battery anywhere else it will be fake and have nowhere near the storage capacity of a genuine one (you might as well have stuck with the dud one). I used to repair phones myself and gave up on genuine replacement batteries bought from third parties.
I recently had my Samsung S8+ battery replaced in the Kingston store for £50 all inclusive. It's made my phone like the day I bought it. Looks like I'll get another couple of years out of it now, which is quite clearly why other manufacturers don't want to sell replacement batteries.