There doesn't have to be a difference, you can throw up a static list of items with price descriptions and a number you can text to purchase things.
This is how we used to sell drugs in college. It was a simple URL you could go to with pricing and you just sent texts to a burner phone to arrange a transaction.
Yeah, this would be a website. Maybe ok for one primitive shop. And for webshops there are tons of frameworks, also possible with reasonable amoumt of work.
But a virtual marketplace .. where different actors make transactions, is a different story. Consider you have a bug and people loose money because of you. It really needs to be solid.
This is how we used to sell drugs in college. It was a simple URL you could go to with pricing and you just sent texts to a burner phone to arrange a transaction.