Any self respecting developer will produce their own assets, or will already have a library of their own assets to tap into.
Your primary audience will be single developers and small teams (mainly students) looking to quickly prototype a game that will likely never see the light of day. This is a population that is fairly unlikely to actually shell out money for assets, unless they are desperate for niche where there does not already exist a body of free assets.
Additionally, you open yourself to asset piracy and asset flipping concerns.https://www.youtube.com/watch?v=5svAoQ7D38k
You are best served by showcasing your talent with free packages, and then leveraging that exposure into a paying position or commission/freelance jobs.
A safer arrangement for making a little extra pocket cash is to try to publish models on, say, the DOTA 2 workshop.
Admittedly, if you do manage to tap into an in-demand market on the Unity/Unreal Asset stores, you have the opportunity to make quite a bit of money. However, the people that are successful in those endeavors are typically people who produce middleware, not models.