How much do you tip Amazon Fresh and Instacart Drivers? If you're a driver, what do you consider a good tip? Do you do straight percentage/amount? Do you adjust by degree of difficulty?

I order about once a month, usually with heavier stuff I can't lug back easily--a case or two of diet coke, for instance, and paper goods. I know they're using their own cars, they're driving in from the burbs to CC, and not getting rich from the job.

Instacart suggests 20% which in my case is usually $15-20 on a Costco order--I feel okay with this. Amazon, which I use for smaller orders, suggests $5 (I do min. $10 cuz my neighborhood is PITA to drive in).

TIA.