No, because that’s not what tips are for? But if you don’t pay for the groceries, then yeah, they should be allowed to not give you the groceries, because that’s how buying things works

But if you specifically agree to pay someone a certain amount of money to load your groceries in advance, then refuse to pay them, it’s totally valid for them to not load your groceries, because you didn’t pay for the service you bought

Jesus Christ on a bike