From Sonic Retro
Wentos (ウェントス Uentosu) is a human travelling salesman encountered by Sonic the Hedgehog and Chip in Sonic Unleashed. He wears an olive green coat and hat, and is always seen carrying a suitcase in one hand and a Chao puppet on the other.
Wentos can be encountered in the game's hub world sections, and sells the player a variety of items which are unobtainable from normal shops. When speaking to the player directly, Wentos seems painfully shy, but when the Chao puppet takes over the sales talk, it comes across as an extremely competent merchant. To be able to buy something from Wentos, the player must act kindly to him so that he can warm up to them and sell his wares. Unlike other merchants in the game, Wentos' buying and selling prices fluctuate wildly at every appearance, so make sure you snap up a good deal as soon as you see it. The first time buying something from Wentos will unlock an achievement/trophy.
Because both buying and selling prices fluctuate, it is entirely possible for an item bought from Wentos to be sold back to him for higher than its current buying price (for example, Chao Chugger could be bought for 20 rings and immediately sold back to Wentos for 100 rings), meaning a player can exploit this to amass an infinite amount of rings, thus allowing them to easily afford everything in the game and quickly max out Sonic's stats with food. This is referred to by players as the "Wentos trick".
In the credits, there are two photos of Chip playing with Wentos's Chao puppet.