When I bought cannabis in high school and college, the primary determining factor for quality was the aroma of the plant.
If it had a strong smell when I opened the bag, that usually meant the quality was decent.
The other major factor for quality was the look of the nugs of marijuana. If you could see visible trichome crystals, that’s also a good sign of quality cannabis. But the final determining factor for good weed was smoking it and reporting on the effects. I’ve had bags of marijuana that didn’t smell great but still got me as high as I needed to be at the time. I’d still choose a better batch if I had access to them, and will always reach for a pungent bag of cannabis if offered it over another bag with muted cannabis nugs inside. I learned in the last few years that what I’m smelling in these good batches of cannabis are terpenes. Terpenes are also found in plants like fruits, vegetables, and flowers. The terpenes in cannabis are also responsible for the effects that are felt in one strain versus another. Specific terpenes like linalool or myrcene might have sedating or relaxing effects whereas other terpenes like limonene and terpinolene might have energizing effects by contrast. If you want to get cannabis products with the strongest effects, you want high THC coupled with high terpenes. I don’t like wasting my money on cannabis products with low terpenes because it feels like the effects are weak. Luckily many cannabis products in cannabis dispensaries come with lab reports that typically list the terpene contents.