I could bother me I was planning to buy assets instead of sell them 
But regardless of that. There are certain games, that will use assets from assets store and nothing wrong with that. Games that aim at more realistic style will do so. Besides more generic assets like rocks, trees (foliage in general), generic props will be used on mass in games.
After all, rock is rock, for most time you can’t really reinvent it.
Oh this category might also include things like architecture. I imagine for most assets there will be at least FBX file and tga textures. So you can customize it, to your needs instead of starting from scratch.
Second option is that people who will sell assets might as well sell their time for specific projects and create assets just for one game. Browsing their assets and portfolio might tell you if it is worth to hire them for job.