I don't sell on here, but I've noticed deterioration as well. Specifically, the algo used to be extremely impressive for delivering similar items in recommendations on listings further down the page (I'm taking desktop view, not apps). Similar by type, appearance, general category, or things people also bought/Watched who'd run the same searches. For people like me, hobbyists, collectors, we often share interests in related areas, so that was a really good service.
I window-shop on here far more than I buy, often out of pure curiosity around my various interests and hobbies, so I have enough knowledge and experience to notice a sharp decline in usefulness.
Over the past two days, for example, I gave the algo enough searches, and clicked through to view enough listings, to tell it I was looking for a specific type of item, and yet it was only turning up completely unrelated things, with different appearance, features, etc., in the down-the-page suggestions.
Chasing an interest and seeing what the algo suggested used to be fun, and encouraged me onto the site more often, in case something cool cropped up. People using your site because they want to browse is the goal of most websites, sometimes it even nudged me into making an impulse buy. Deterring a user who's expressed an interest, and is willing to be tempted, isn't considered a good thing by most businesses...
And with search becoming increasingly useless and dumb, the algo's recommendations were often the last hope left to find used, one-off, vintage items which were listed by ordinary Private sellers who don't jump through any hoops to promote their items, or which had been listed for a longish amount of time.
Okay, I'm just one user, but that's quite a serious problem if you scale it up.
