Mmmm.
As you probably figured on the other threads you posted, HikaShop cannot yet handle different groups of users.
For a list of local installers, you could cheat the system by using shipping methods as a mean to select local installers based on the state/country entered by the user (you can also modify the zones to display areas instead of states and use those areas as zone limitations for shipping methods.
It's not straight forward though, as it wasn't built to be used that way. Plus, if you have at the same time real products that you want to ship which real shipping methods, then, you need to make sure that you will display one time of shipping methods and not the others by using a big difference in weight in order to set both apart but then if the user tries to buy an installer and a kit on the same order, it won't be able to display both....