I had something similar happen to me recently. Two different vendors used the same base texture for their store items (purchased through a commercial re-sale license and modified). I don't mind that but what I do mind is when the vendor isn't up front about the texture being based off another one. Now I have two (admittedly excellent, but EXTREMELY SIMILAR) textures. If I had known the second purchase was based off the same commercial re-use texture, I probably wouldn't have purchased it.

I have to say, though, that it seems pretty common for texturers to use the same base texture over and over. I can see it plain as day in many of the preview images in the store. For me it depends on price.. for 10 bucks or less, I am not gonna complain. But 25 - 30 dollar texture packages? I expect completely new pieces each time.