How do you handle customer complaints about appointment windows that get shifted?

We've been seeing an uptick in customer complaints when appointment windows need to shift—whether due to emergency calls, technician illness, or jobs running long. While we always try to communicate proactively, the reality of field service means some disruption is unavoidable. I am interested in hearing how other teams approach this from a customer relationship perspective. Specifically:

• What communication methods have you found most effective for delivering schedule changes?
• Do you offer any form of compensation or goodwill gesture when windows shift significantly?
• How do you distinguish between minor adjustments customers tolerate versus changes that genuinely damage trust?

From an operational standpoint, we are also weighing whether to build buffer time into our scheduling to reduce the frequency of shifts, or to maintain tighter schedules and accept that some rescheduling will occur. Another way to think about this trade-off is whether predictability or throughput matters more to your specific customer base. I would appreciate hearing what has worked—and what has backfired—in your experience.