Isn't that the biggest issue, it's like the Wild West out there at the moment, all the double glazing salesmen seems to have jumped onto the Solar bandwagon.
I really want to do the installation myself, apart from maybe the last connection back to the grid, which as usual is shrouded in the terminology, has to be a competent person, but as usual there is no definition of what constitutes a competent person, the Installers out there will try to convince you that you have to have qualifications, but I don't think that is quite correct, however your provider may insist they are.