Looking to sell in your dispensary? The greenest way to make more coins for your stuff is to upgrade your shop, man! With every level you gain a multiplier! Wicked, right?
The multiplier DOES change the top end price at which you're allowed to list the item. (eg. you can sell Purple Buds for 2x the base price!). This multiplier DOESN'T change the amount you get when someone buys something from you.
So go forth my young POTrepreneur pal, and start raking in those coins!