There are two types of shops, vending machines and original shops. Vending machines consist of rental land with items in it available for anyone to purchase at anytime. Original shops are shops where items are on display but must ask the store owner to buy it. They then will go through a cash register trade.
Vending machines are more convenient, especially when the owner is offline or when the shop is crowded, however, it is very pricey in the long run as it costs 500c for ONE bumper and 500c for a bunch of foundation blocks with won't last long if they are continuously destroyed. However all you need in an original shop is maybe some glass blocks, items to sell, cash register, signs for prices and maybe a few decorative blocks to make the shop look appealing.
Extra blocks can be used to enhance your shop. Blocks/items may include: