If we take you to be serious that using a firearm is a last resort, at what level does getting ripped off rise to a last resort?
Because if you're getting "robbed" you already have a gun in your face. If you're getting ripped off, then it's not life or death, is it? If you showed up obviously strapped to your dealer, would he do business with you, or assume you're going to rob him?
So, again, what point is there, mr. not a gangsta, in bothering with a firearm?
I'll point out that if you have a firearm while buying drugs, depending on the state you risk multiplying your felonies. I mean, even if you legally own, and have a license to carry, just having a firearm on you while committing a felony could make your life much more difficult if you got popped. Shit, I wouldn't be surprised if they could argue intent to distribute, since you were clearly prepared for trouble, and not out to just buy some weed.