I've worked these 1099 grocery delivery gigs and you get paid around minimum wage to lug these very heavy orders of water and juice up stairs, all while adding miles to your own vehicle and bearing the full risk of injury because you're an independent contractor. I hope you tip them well at least.
I wish no one would tip them. Then they'd quit working for minimum wage, then the costs would go up, then I could see the actual cost of the service and make a decision to use it or not.
a tip for an unusual order/circumstance would be fine. Say if you ordered a 50lb bag of cat food, and live on the Nth floor, and the elevators are not working.