Every listing needs a feed map
Document which platform exports to which destination, when the system last fetched each feed, and which calendar is authoritative. A missing reciprocal import can leave one channel blind.
Polling creates a delay
A reservation can be accepted before another channel imports the block. Faster polling reduces but does not eliminate the risk. Keep native notifications enabled and define a manual conflict response.
Know when you need a channel manager
If the business needs near-real-time inventory, rates, restrictions, payments, and unified guest messaging, iCal alone is not sufficient.