Tracking office boys and controlling their mileage is a critical job. There are few suggestions. Whatever measures you might adopt you could ensure the desired advantage only if you follow him, which is not possible. However petrol allowance can be controlled by fixing mileage allowance, like auto meter. This is possible by fixing distance from point to point and compute the mileage allowance Rs.x per km. Though it's not possible to accurately calculate atleast to some extent can have control.
Reg.time control, if you he has to travel hoping from your office to clients' place, ask them to call you or your supervisor from every such client immediately after delivery is made and record the timings in a log book. You can cross check by calling the clients or talking to them on your office boys' mobile at the time of delivery itself to record the exact time of delivery. Video call could help. You might as well arrange a prepaid office mobile for them (after collecting some deposit money) Abnormal gaps, if any can be tackled once he returns to the office after finishing the days' routine.
10th January 2019 From India, Bangalore