Not getting bids from at least 3 A+ BBB rated and CSLB licensed contractors. We are all a little different. Sullivan’s focus is on quality installations and customer service. As a result we are not the cheapest. This may or may not be what you are looking for.
Not hearing all payment and ownership options: cash, lease, finance, HERO, PACE… Some companies ONLY sell leases, you need to hear all options to know which is best for you. Yet another reason to get multiple bids.
Moving forward with a contractor who does not have at least several years experience and hundreds of installations. They will all tell you they have enough experience; it’s up to you to do your research and find out for yourself.
Getting tricked into buying from a ‘front’ company who is really a reseller or call center. They will tell you just about anything to get you to sign, then sell your installation to the highest bidder. You might not even know until something breaks and nobody honors your warranty.
Letting a non-solar contractor convince you they can put solar on your roof. Your roofer or electrician sees easy-money in this, but do they know AutoCAD design, solar permits, local and state law, 20 year warranty, finance options...