From PinataIsland.info, the Viva Piñata wiki
Do you need a new watering can? Does your new piñata need a new home to stay out of the rain? Head to the village where many shops are available for you to buy, sell, and trade. All of the shops exist in a local village on Piñata Island.
The in-game shops are where you can trade in your piñata for currency to buy bigger and better things for your garden including seeds and plants. You can also buy costumes and accessories for your piñata, upgrade your tools, hire helpers for your garden, or even buy pets, such as cats or dogs.
You’ll be able to buy new objects both with your chocolate coins in game, and also with Microsoft Points in the Xbox Live Marketplace.
Helpers are available for hire at Arfur's Inn. You can hire up to five helpers to assist you in your garden. If you need more help with one specific task, such as weeding, you can hire multiple Weedlings, and even rename them (which unlocks an achievement).
The tinkerer at Bart's Exchange can transform one item into another for you. Items that have been transformed have varied uses. From a color variant to even taming a sour. There are three different ticket levels, with a bronze ticket giving a 25 percent chance of success, a silver ticket giving a 50 percent chance, and last of all a gold ticket has an 100 percent rate of success.
Costolot's General Store
Costolot's General Store sells seeds, produce, fertilizer, candy, fencing, and other important items for your garden. You can also sell unwanted items to Costolot for chocolate coins. After selling to her once, you will be able to sell items to her more quickly by hovering over the item you wish to sell and pressing . (Hint: Fence sections do not allow you to do this, but by selecting the Sell option on another nearby item, you can choose to sell fence sections instead. This is much faster than going through the menu to reach the store.)
Doc Patchingo is the village piñata doctor, on call 24 hours a day. After visiting his shop once, you will be able to call Doc to your garden by selecting a sick piñata and pressing .
Fanny Franker's Post Office
Fanny's Post Office is where you can send piñatas, money, seeds, and garden items from your garden to a friend's garden via Xbox Live. Also you come here to receive packages from friends. You can also send yourself crates (No need to use Xbox Live) of pinatas, plants, homes or garden items. These can be sent between your gardens or just held until you require them again in the garden you are currently playing.
Gretchen is a hunter that can track down lost strays, or fetch a wild version of any species that you have seen before. So even if you have lost (or traded away) all piñatas of a particular species, you can still get another by paying the hunter to fetch it for you.
Ivor Beggar shows up in your garden as your garden become more valuable (at level 12). If you are charitable, he will leave you alone for a while. If you give him enough money (1000 coins) he finds he has enough to become a trader and later will open his shop in the village. Ivor Beggar transforms himself into Ivor Bargain! His store carries many very unusual items, and many more are added as your garden improves.
Miss Petula's Paper Pets