They will probably take a hit on some returns. Some kid grabs a perishable that the parent didn’t see, and the parent returns it three days later and it’s past due in one day, so it’s a loss.
Amazon will swallow the loss and smile, because it brought the parent back again and the parent probably bought another 4-5 items while making the return.
Once they have traffic enough, prices will gradually rise so the returns will matter even less. And they will get better at flagging weird purchases on the spot. And parents will be better trained to keep their kids from grabbing stuff.