I've seen this too. But I'll be searching for one thing, and look in the "related items" when I click one of the results and see an item that should've shown up in the results, a lot of times better than the one I clicked on, and I'm scratching my head wondering why it didn't show in my original results anywhere. I've learned to pay close attention to related items these days and I've scored some wicked deals that way. Somehow eBay's relationship algorithms are better than their search algorithm. Bonkers.

But I haven't noticed any issue with operators. You just need to be careful when using parenthesis not to use spaces after your commas. For example, say I wanted to find Colnago pantographed seat posts and stems, but avoid getting hammered with all the damn chainrings and cranksets, I'd search for

colnago (panto,stem,post,seat) -(ring,chain,crank,crankset,chainring)

Basically telling it search for [colnago] items with [panto or stem or post or seat] in the title and excluding [ring or chain or chainring or crank or crankset or chainring] in the title.

It's not perfect. But say you were searching for Treks and only wanted to return auctions with very specific models (560,660,760), and wanted to exclude results that have totally unrelated words (antelope,multitrack,mountain), it's totally possible.

I seem to remember it was much more flexible. Same with Craigslist keyword alerts. I swear both used to accept pipes | but maybe I'm crazy.