They Lease. Typically when you try to sell your home, the new owners have to accept the abusive lease transfer terms or likely, you'll pay a massive penalty.

They don't buy from a real installer. Companies that don't install what they sell usually pass the warranty on to a subcontracted company, which is usually just a bunch of inexperienced people working for pennies, potentially costing you more to fix poor-quality workmanship.

They don't add a battery. With the new NEM 3.0 regulations, the electric companies pay much less for the extra energy your panels produce than they used to. Thus, not having a way to store that extra energy for later use (or in case of a power outage) costs you more on your electric bill.

They choose price over value. Quality pays. Cheap equipment and cut-rate outfits are a sure-fire headache. These companies tend to disappear quickly, right along with your warranty. Find a company with 10+ years of experience and a proven track record of success.

They believe "Free Solar" is really free. When you see ads for "free solar", RUN! On a significant purchase like solar, going in with dishonest companies can cost you big.

They aren't aware of financing options. Everyone knows about the federal deferred 30% tax rebate, but many forget to cash in when they file their taxes. A company like HDM gives you 40% off everything upfront using a little known (legal) strategy.