I Decree

[billy]

weed legal but must be sold through a registered shop

wouldn't it be best to make it illegal to sell/buy weed, and instead allow each citizen to grow up to "n" plants for own consumption?
no money involved and no one making profits.

growing and selling the product you can regulate it so no shit gets through. and of course you'd be allowed to grow your own within limits for personal consumption. not everyone would want to grow their own, the stink alone is outrageous. plus it would be a revenue stream that could offset the countries imports etc. there would be an annual contest to see who has developed the best strain with awards an shit.