I have experienced this also because my company is a supplier of truck mounted aerial work platforms. I do all that I can to make sure that the customer is clear on how much the truck will weigh upon completion ( net weight ) and how much is left over for tools, materials and workers . ( gross weight ) We and the owner of the truck also have to be careful of the loads we put on front and rear axles because they have maximum load ratings also. It is unfortunate that the end user was not told up front what his trucks carting capacity is BEFORE the truck is completed and delivered. In general we can and I am sure most other installers will be able to give you approximate weights of the truck before the job is started.