...and that's rendered ineffective by SaaS bot companies that take your account logins and payment details and places the orders on your behalf, for a fee of course[1]. The economically efficient solution would be to auction off the slots, so at least the grocer is reaping the profit rather than some third party. It also has the benefit of capitalizing the grocer so they can hire more people and/or buy more equipment so there are more slots in total. Also, if it bothers you that some FAANG programmer can afford deliveries than some old granny, this can be alleviated by reserving a certain % of the slots to "needy" people (eg. old, disabled, sick, immunocompromised) subject to validation.
[1] kinda like https://en.wikipedia.org/wiki/Domain_drop_catching