Probably the biggest thing to watch out for is getting locked into a solar lease. If possible buy your solar PV equipment outright. Solar leases come with penalties for early termination. I work in the solar industry, in the training sector and write to a global audience on everything solar PV. It would be a conflict of interest to recommend specific companies. It's best to gather 3-5 quotes from large to small solar companies for the best balance of customer service and cost. Energysage is trusted by many Redditors to compare solar quotes by location, get $25 off by clicking this link. For another option in gathering solar quotes, EnergyPal helps to leave the final decision of the solar company selected, totally in your hands. Get a $500 gift card from them by using the link mentioned. Always ask these questions of any solar installer when gathering your quotes :

Are you approved, licensed and insured to operate in my state/county/city?

Ask for their license and policy number and verify that it’s in good standing with the appropriate licensing board and insurance providers.

Is my roof a good fit for a solar PV array?

Realistically, most solar panels can be arranged to capture the greatest amount of energy with adjustable racking technology and other assessment tools. In the end, some homes will have better solar coverage of their roof over others. Using a tool like Project Sunroof can help you assess on your own and without a salesperson. If your roof is covered in shade by large trees or a nearby building, north facing or in poor condition it may be not suitable for solar installation. Installing a new roof and solar system at the same time can be a cost effective way to combat climate change and lower your carbon footprint.

What happens if I want to sell my property or move out?

Look for specifics in your contract and ask for them to be explicitly noted. If there are any penalties or fees you’ll see them here. Another important point is the ability to move out of the property and rent it to tenants. In this case, the options should be stated as applicable. Perhaps you wish to have your tenant pay the electric bill but you wish to continue with the financing payments for the PV system. Learn all of these details up front and from the contract’s top to bottom.

Do you use contractors to install the equipment?

Using a third party contractor can bring opportunity for uncertified or unlicensed/uninsured workers on your property.

What type of warranty does the system and install come with?

Warranties and guarantees can vary greatly. They can exclude certain components and not provide a point of contact should something go wrong. Get as many details in writing as possible before signing a contract.

What is your estimated timeline for project completion?

Timelines can vary greatly and can influence total cost. Watch out for the estimated timeline and that it works with your schedule.

Can you provide the total cost of the system to me in digital or paper format?

If you are looking to finance or lease your system ask about any required down payment and how much monthly payments will be. Any state/federal/provincial tax credits/benefits should also be detailed here. We strongly advise readers to own their equipment outright to avoid any additional hidden costs or penalties/fees should they want to exit the contract or sell their property.

https://ecotechtraining.com/blog/how-to-find-a-solar-installer/

There is also more information on finding the best solar installer in the link mentioned.