They are a business and will demand you to be professional in your approach. Telephone ahead and make an appointment to meet with the storeowner or manager. Do not show up with kids in tow. Be prepared with info and prices. Most stores will need the items prepackaged.
Pricing is important.
Remember the store needs to make a profit. You need to make a profit. Yet, the item still needs to be at a reasonable price. If all goes well, and the store wants to carry your items, they may offer to purchase outright. This is good for both sides.