The cost of an item is the same for food stamp or pay-your-own shoppers, it's true, but I was told by a retailer several years ago that the government only reimbursed a percentage of every food stamp 'dollar' spent.
Was I told wrongly?
When you buy with a food card (no state uses the ‘food stamp’ any more) you cannot be charged local or state tax on the groceries.
Maybe reimbursed from the Fed to the State Govt. but the individual grocery retailer gets full price from the State. There is no downside for the retailer.