For a car that will not start or has a warning light: send the symptoms, when they began, and the vehicle details. Ask whether the service accepts that make and the proposed diagnostic work. You can request an assessment without deciding that a battery, starter or another part has failed.
For a commercial truck or trailer: identify the affected unit and whether it is a power-unit, trailer, engine, electrical or air-system concern. Include any existing fault report. Ask whether the mechanic has the appropriate equipment for that vehicle and job. A fleet yard visit and a roadside response require different access arrangements.
If you are considering the featured Langley service for a truck breakdown, its roadside truck repair page explains supported faults and the details to send.
For a vehicle you are considering buying: ask what the inspection covers, what report you receive, whether a road test is included when feasible, and how the seller will provide access. Confirm the vehicle type and inspection terms with the provider before treating an inspection as booked. An inspection is a specific scope of work, rather than a promise that a used vehicle has no faults.