Re-Tail, known as R. Parker's in the Japanese version, is a retail store run by Reese, a pink Alpaca, and her husband Cyrus, a blue alpaca. You can sell things there, and you can buy things that your villagers have put on sale. You can also have furniture customized, and you can check the stalk market prices there.
Reese, the pink alpaca, offers the best selling prices in the game. You should always take your items to Reese to sell.
Be sure to check the sign next to the front door of Re-Tail. Each day, it displays an item that Reese will pay double for. Sometimes the listed item is specific item (for example: sharks), or a certain type of item (for example: hats).
Rather than sell items directly to Reese, you have the option to put an item on display for sale in the flea market spaces throughout the shop. You can set your own price. Then, if a villager comes into Re-Tail while you are there, the villager might notice one of the items on display and walk up to it. When this happens, you can talk to the villager, to convince him or her to buy the item.
When you put an item on display, Reese will ask what price to set, and there is a suggested Re-Tail price as the default. Generally, villagers are willing to pay a little over four times Reese's suggested price. So, for example, if the default price is 200, try selling it for 800 or a little more. Your yellow feng shui probably influences how high a price your villagers are willing to pay for your flea market items. If the price is too high, the villager will refuse to buy the item when you ask them to.
Cyrus, the blue alpaca, wakes up after you have played for seven days, sold 100,000 bells worth of items to Reese, and have 100 pieces of furniture and 50 clothing items in your catalog. (Items are added to your catalog as soon as you put them into your inventory, even if the Nooklings' shop doesn't have a catalog machine yet.)
On Sunday mornings, a brown boar named Joan will sell turnips in your town. During the week, Reese offers changing prices for your turnips. You can talk to Reese to find out her current selling price for turnips. If you check the prices each day, you might be able to predict when the prices will spike and you can make a big profit. Find out more in the stalk market guide.