Dave makes a great point, it would be nice if the site could set standards to allow professional companies while keeping out every Tom Dick and Harry with a ladder and a case of walmart lights.
Christmas Light Leads - I know you said you confirm insurance, how far do you guys check? Do you just accept insurance paperwork? do you confirm with the carrier that the policy is active and covers holiday lighting? This alone should cut out alot of the riff-raff.
Dave one thing I do is every customer I meet with gets a tri-fold I had printed up, it basically goes over our services offered but a majority of it explains the importance of insurance and the legality issues the property owner could face for hiring a contractor without it. It walks the customer through how to check that the company in registered with the state, carries the proper insurance, and how to check for proper licensing as well. I also made sure to include sites that have court cases in which homeowners lost big $$$$ due to law suits from injured contractors or damage caused by contractors. It really catches the property owners attention and since I started handing them out I have been closing alot more contracts, I still lose to many but at least I'm losing them to legit companies.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!