They are the same model. They both buy stuff, do some stuff and then re-sell the same stuff but with the modifications they made. In the case of a trading shop

They are the same model. They both buy stuff, do some stuff and then re-sell the same stuff but with the modifications they made. In the case of a trading shop, the stuff they do is playing the market liquidity, collecting interest, arbitrage, etc... Sure there are some evil ones, but other businesses have those too.