Do I need a smart contract to process payments between customer and merchant?

I started writing a smart contract that would essentially act as a 3rd party and would process transactions between a customer and a merchant. However, in the middle of development, I realized that a smart contract is not needed as any token has it's own contract to process transactions, and I can query the blockchain to see whether a transaction has been made. Am I correct or is there something I'm not seeing?

EDIT: Most of the stuff would actually happen in a database so the only requirement needed is to process payments with an ERC20 token.

I'm new to all of this, so any advice would be welcomed.