An AMC is worth having, but the value sits entirely in the specifics. Two contracts at similar prices can differ by an order of magnitude in what they actually oblige the vendor to do.
Response time must be defined and measurable
"Prompt response" means nothing. Look for a stated number of hours, a definition of when the clock starts, and whether it counts working hours or elapsed hours. A four-hour SLA that only runs Monday to Saturday during business hours is a very different product from four hours around the clock.
Know what "parts included" means
Most contracts that advertise parts cover consumables — connectors, adaptors, power supplies — and exclude cameras and recorders. That is reasonable, but it should be written down. Ask directly which components are covered and get the answer in the contract rather than in an email.
Preventive visits should produce a document
A maintenance visit that leaves no written record is difficult to distinguish from a visit that did not happen. Insist on a health report per visit listing each device checked, its status and any recommendation. Over a year this also gives you a genuine picture of which hardware is degrading.
Storage retention drifts, and nobody notices
Recording settings change, cameras get added, and the retention window silently shrinks from thirty days to eleven. A good AMC verifies actual retention at every visit and reports it. This is the failure we see most often on systems that were correctly specified at installation.
Check the exit terms
Make sure you own your footage, your configuration and your admin passwords, and that they are handed over if you change vendor. Systems locked to a vendor account are a real problem at renewal time, and the moment you discover it is the moment you have lost your leverage.