Is the store also letting you sell beverages?
I don't work with our local store b/c they have their own deli, and try to sell some of their own product. They also want to sell the beverages and they want me to use their meat, which I feel is a lower quality than Sam's clubs and just as expensive at "their" costs.
Be careful with the meat you use. You may be an amazing cook, but if they are giving you substandard meat, or perhaps pork cushion instead of pork shoulder then you will spend more and have to work twice as hard to build your reputation.
In trying to build a customer following, if the first 50 sandwiches you sell are fatty, or grisly, taste tough or are anything but amazing, you are in trouble.
Lastly, you are the BBQ professional, You are the BBQ entrepenuer, You are the Pit Master, Don't let the Store dictate the rules to you. You can work with them, but You need to be in charge of ground rules like freebies and such.
I did this once with a flea market, I pulled out after three of the six months it was open. It was not worth my time or money to attempt to work with someone who'd never picked up a thermo-pen to tell me how my business would be more successful, yet listen and watch them try to cost me $$$'s.
I apologize for the ramble
Hopefully their is one or two things in this ramble of my experiences you can use.