A published price list
A sheet of starting prices lets you compare and plan. Ask what is included and what is extra.
A licence you can check
Ask for the BSIS licence number and look it up.
Discretion and scheduling
For homes with staff or stores with opening hours, being able to book a time and share gate codes privately matters.
High-security options
Restricted keyways, Grade 1 deadbolts and smart locks should all be available, with clear explanations of the differences.
Clear terms
Know who invoices you and who gives the warranty. This service's terms explain that work is done by independent contractors.