From the Super Mario Wiki, the Mario encyclopedia
Westside Goods is a shop in West Rogueport. At first, the shop appears to be normal. It sells items that are usually more expensive and more effective than those found at the Toad Bros. Bazaar in Rogueport's main square. However, the shopkeeper, Peeka, is actually a guard of sorts for the Pianta Syndicate. Peeka will only let Mario into the Syndicate's headquarters if he passes two tests. The first is in the form of buying a Dried Shroom and a Dizzy Dial respectively. The second is a question asking Mario's favorite color; if he answers yellow, Peeka will be able to tell that he has business with Don Pianta and allow him through.
Best selling prices