I discovered this with doordash during the pandemic. They would flat-out not bring things, or would make insane substitutions (one that springs to mind is maple syrup for flour, as though if i have enough syrup pancakes will just happen in some sort of drizzle-down economics) and when you talked to support they would refund the cost of the item as account credit but not the delivery fee. Which means that not only did they not unwind the transaction after they failed to deliver their part, the only way for me to get what I ordered in the first place was to order a second time and pay them a second delivery fee.