I wonder if the relevant units of government creating standards for these jobs would help.

Plumbers and electricians have to be licensed in many areas. I’m sure building codes require building permits.
Wheels of government take time to turn, but requiring installation companies use licensed installers, and handling the licensing and vetting in the same way electricians and plumbers are handled is a good place to start. Definitely always loopholes in the construction business, but a formalized and licensed profession is a way to improve pay.