I think, because we're all inspired from the same sources, there's always going to be a little overlap. I usually do a little bit of searching before something goes from my "to-do" list into my editor. I try to save myself time and heartache.
It's still hard sometimes. I made a pattern and wad shocked it hadn't been done before, so I listed it. Three months later, it appears someone DID, and just had their store temporarily closed for a while, lol. It happens.
That being said, I did come across someone's store... a little of katiekuthroat, weelittlestitches and even Steoch. It was just SO brazen, and there's no real way to stop it (much like the pattern lifters who think a few bucks isn't worth it when they can spend a couple of days breaking down an image and stealing it).
Just know that they're in it for the quick buck and will probably burn out as quickly as they went pillaging, lol
I used to search regularly for my pilfered stuff. Once I got over my brain exploding, I decided it wasn't worth the heartache.