It is not the tech who sells the work that is a service writer. The tech is expected to be honest, as is the writer and the customer too. Customers try and work you for every penny, often implying that a shop down the road quoted them 20% less on the same job when the truth is that they never spoke to the shop down the road.
We all need to make our money on every job.

For example, a truck with 180,000 miles should be looked over harder than one with 80,000 for worn parts.

If the goal of the customer to have a reliable ride as trouble free as possible, ball joints with 180k do not need to be tested for wear, they are worn. Give the customer the choice to have the local neighborhood shop fix it or let the guy at the truck stop in the middle of nowhere do it taking time and money from your vacation.
Repairs cost a ton more than maintenance.

A auto tech is no less honest than a AC saleman or any other job. If you rip folks off you will be out of work.

SD