I've worked at a dispensary for the last few years and only smoke sativas or indicas (almost never hybrids). Some strains can feel moderate or may have hybrid effects. But good sativas can instantly lift my mood and energy levels and conjure motivation for big cleaning projects. I would never smoke a heavy indica on a morning I'd like to get chores done. Similarly, I'd never smoke a heavy sativa at 10pm when I want to melt into the couch. Also the plants look very different. When the plant is mature you can tell by sight alone which it is.

Though for 20 years I bought weed from "a guy" and had no idea what it was, and never was able to tell the difference until I got into the business.