Would this work with no risk? Say I see one vendor selling lsd for $4 a tab with free shipping. I go to another market and make a listing for $6 a tab. Then when I receive an order just make an order from the $4 guy and use the buyers address. Is that a crummy thing to do? I looked into doing something similar back in the day with china imports on ebay but, never tried it.
There is no such thing as 'no risk.' If you don't have the product in-hand, you're at the whim and circumstances of the supplier...for every single order you receive/place.
As to the rest, if the person you're buying from is (quite clearly) selling individual, or other low-number, hits...prospective clients will easily stumble-upon your 'supplier' and go with him. In essence, your supplier is also your competition. That's a recipe for going nowhere. You'd have to make 100+ successful sales just to make back your vendor bond, depending on market. And that's if every single one of those orders goes-off without a hitch. Which they won't.
If you want to get into the game, then get into it for real. Be the guy who sells for $4/per by buying large quantities at 'wholesale' prices and get your hands dirty.