I've seen several different vaporizers, but from what I understand the high-end quality ones are excellent.
If I saw it correctly, you place your bud into the space provided. It then heats up the marijuana until it's hot enough for the THC to become psychoactive, and the bud releases the THC into the air. (without actually igniting the bud, just heating it up) Then you have a hose or whatever the mechanism on that vaporizer has, and you inhale basically steam, almost pure THC, with little to no carcinogens.
So in theory, if you had a large enough vaporizer, you could place an entire harvested bud into the heating space, have it extract all of the THC out of the bud without burning it, and then turn it around and sell a placebo...
That's my understanding on the high-class ones, though I could be wrong. If not, I just won the nobel pot prize.
Maybe you could make a homemade one.....
LOL I just made this theoretical one in paint, I guess you'd just heat it up hot enough to get some vapors and not hot enough to burn the bud to bad:
Actually, another Idea, maybe a pressure cooker would work better?