Badly designed API is badly designed.
Apart from the obvious rate limiting, and limiting the number of slots one user can book, an astute designer might think to, for instance, not allow booking of slots the day they are first posted but instead take requests for that slot and assign them after 24 hours (or even longer, if the slots are well in the future), either randomly, or to whichever person last had that slot the longest time ago, for fairness, so that everyone gets a chance.
It's not like booking systems for time slots like this are a novel thing, and it's exactly the reason our local sports centre stopped taking bookings online for the badminton courts because the same people would book the Sunday slots every week, and only turn up half the time. Shock horror - you now have to call them or go to the front desk and book a court.
Biting the hand that feeds IT
