I agree that dangerous things can be done by peoplo that don't know what they are doing. But the same thing has happened to the automotive industry years ago.
Of course it is a good argument but in my opinion the main reason for the manufacturers is market protection, not safety. At least here in the netherlands: We would be very happy to get trained but for most brands the training is just for their own technicians.
They really don't like it when they sell a new forklift with little or no profit, have to make costs to repair warranty issues, and at the moment they can make money, the costumer chooses for an independent repairer.
What they have to do and what we have seen in the automotive industries (after RMI was introduced there): make it easier for the costumers to choose for official dealers: Tell them the dealer can fix it better, has more know-how, and as a result have lower costs because of better maintanance. Costumers don't walk away when they are satisfied!
Until this has changed: we will be very happy to serve their costumers.
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