What do I do when I'm overbooked?
Short answer
Call the customer before they call you. Honest update, real new ETA, and an option. They forgive late, they don't forgive surprise.
Get ahead of it
The second you know you can't make it, call. 'Running behind, can be there at X' beats showing up an hour late ten times out of ten. The call is the trust, not the time.
Offer choices
'We can come today at 4, or tomorrow morning first thing. What works better?' Giving them control returns the goodwill you just spent.
Ask your version of this question
This is one business owner-tested take. Your shop size, trade, and team change the answer. Ask the exact version inside Ask a Shop Owner and get a response grounded in how owners like you actually handled it.