I have noticed this myself over the past year. It is clearly done intentionally to encourage more sellers to use Promoted Listings, paying eBay more fees.

First, I noticed quite a while ago that, the search brings up, as you say, random results in their hundreds. For example, you search "Tina Turner Foreign Affair White Vinyl", with a view to compare pricing or purchase this LP on white vinyl and it will bring up ANYTHING with ANY of those words in, ignoring the word "White". This is a nightmare for sellers and buyers.

More recently I have noticed that even when sorting by "Lowest Price + P&P", eBay disregards this and will show more expensive items at the top of the list.

And in the past few weeks, I've noticed that when searching for items, all sorting options work, EXCEPT "Lowest Price + P&P"....  Coincidence? I think not. So to do a price comp, You have to sort by MOST expensive item, scroll all the way to the end of the listings, and work backwards.

Come on eBay, if you're going to try and cheat us, at least do a better job of trying to hide it.