As yall might have figured out by now, taxes and protocol varies by STATE--just like most little laws involving taxes and taxable behavior--when, where how you can buy alcohol for example.
In Tennessee, I take the truck pumps whenever possible. No problems, no price differences, no phone/radio necessary.
Also in Tennessee, Sunday beer sales vary by location, NO wine in beer stores, and no wine/distilled spirits on Sunday anywhere--except wine AT the winery.