The whole tax thing has been debated before (of course).
The state must be very careful on its taxation procedures. I believe no tax should be had on cannabis as it has no detriment to society like alcohol and cigarettes (drunk driving and lung cancer to name a few). However, if the state doubles the price of cannabis so it's say $200 weed $200 tax for $400 total, you'll see a HUGE black market for cannabis. Just like we have now. The tax is considered too high. However, if they tax it at say 10% of the selling price, and that ends up being $20-$50 in total, then most will likely pay it as the tax is 'acceptable'.
There's black markets for cigarettes and alcohol already for those not wanting to pay the 'tax', but the cannabis black market is much larger already because its already illegal to sell it to begin with in most places, so we have the "head start" approach where we already can buy it tax free so no real reason to bother paying it if it does come up.