At risk of repeating myself, do not do it without charging for the report and its not a quote but an estimate and make sure the insured know that they are paying for it NOT the insurance company, otherwise they will get you round and ask you to invoice the Insurance company for your time which of course they will never pay.
This way you get rid of the time wasters and the entitled and instead only get qualified insurance leads.
As a side note, nearly everyone has an excess to pay usually between £50-£100, explain to them they can use this to pay for your report and put it against the excess which the insurance company do recognise as a legitimate use, this usually calms the resistance and ensures you get paid but it also gets you in-front of the Loss Adjuster or Insurance claims clerk which could result in additional work.