Homeowners pay nothing. Approved trade firms pay a subscription if they want to receive introductions from people who have asked for alternative quotes. That payment never affects your comparison, the price ranges or what your result says. Firms cannot buy a better result for a homeowner, and they never see a quote you have not chosen to share.
Every firm is checked before it can be introduced to anyone: company register entry, public review presence and documents such as insurance. Those checks confirm the basics. They are not a recommendation.