Build the network before you need it
The time to find a 24/7 plumber is not when the boiler fails on a Sunday. Build relationships with 2-3 trusted plumbers, electricians, and handymen BEFORE you need them. Pay for small jobs to build the relationship.
Hourly + materials, not project pricing
For ongoing maintenance, an hourly rate (£40-£60/hour) plus materials at cost works better than per-project quotes. Faster response, no bargaining each time.
Guest-facing communication
When something breaks during a stay, the guest doesn't care about the contractor schedule. They care about when it gets fixed and what compensation they get for the inconvenience. Have a policy in writing.