I would happily pay taxes on weed purchased from conventional businesses, but I wouldn't pay taxes on any other transactions (buying from friends, etc). Tax evasion is not so much a problem if you are not a business owner and don't keep records. If you were living in a really expensive home or a high scale apartment, and driving a BMW, and there's no way your regular job could afford you such lavish lifestyle, then maybe that would bring on the scrutiny.