According to Jason King, author of the Cannabible Series, most of the weed from commercial producing countries such as Mexico, Jamaica, and Africa would have been fantastic if harvested, cured, and handled properly.

For instance, in the countries I listed, a common practice is to hang the buds upside down, outside to dry. Obviously it's very hot there. It turns the weed brown. It's mostly never cured. Then, when the buds are dried they are all thrown around, and tied together, etc... and most likely transported. From then on, it gets packaged in many different forms for smuggling large quantities into the country. They jam it into different sized containers and boxes, sometimes making brick weed, sometimes just having super compressed brown buds, by this time, most of the trichomes have fallen off. Think about all the kief you get from grinding up your weed in your grinder. Well, this weed has been tossed, thrown around, and jammed into random packages, obviously losing a HUGE majority of it's trichomes.

Then, by the time people buy either bails, pricks, or large quantities of this, for a low price, they handle it even more. Selling ounces to people, only to have it get bagged again into smaller amounts, until it reaches it's final destination, in which it's terrible.

That's why everyone should grow their own.