I believe that you have a moral obligation to tag the truck out if you feel, in your professional opinion, that it is unsafe. It make come back to bite you either because:
A) Your analysis was incorrect
B) The client may be upset with you and choose to use another source for their repairs.

Just as I cannot go to the Ministry of Labour and report that certain people are not competent to operate the forklift, who are certainly doing so. The repercussions can be a blow to my business. I come out looking like a RAT and if word gets around, I am in trouble.

I stuck my nose into a client's business spring of last year because their data plate on a 5000lb stand up CB read 2600 pounds. They purchased this truck to lift pallets weighing as much as 3700 pounds. It is illegal to exceed the rated capacity of the lift truck, and that was what they were doing, unknowingly. Now possibly they could acquire these loads up to a certain height, but the data plate showed the height being 240in. Was not worth the backlash I received from a couple of other members in the technical arena, and I probably should have let it pass.

In this business, you do the right thing, and you never win!