What turns herb into a grade of weed depends on 3 things:
Genetics
Grow technique
Processing

Think of it as a whole range with all possible combinations:
Good genetics grown well and processed carefully will give you the best herb, known as 'headies'.
Decent genetics grown decently but then kiefed off and vac'd, such as the process of turning M39(?), a good strain, into Beasties, which I'd never smoke, well the good stuff gets lost in the crappy processing.
Commercial-style genetics grown carefully will still give you a lot better product than the herb they came out of in many cases, since you will probably let it ripen more fully and then cure it well.

Plants grown from bagseed that is known to have been grown indoors are very very common to see among amateur indoor growers. I'll admit it; I've grown out seeds from The Beast and been satisfied with the result. Once you get your technique down, don't be surprised to get far better product from bagseed than you ever saw it come out of.