Well it seems mighty suspicious when someone asks for £300 cash upfront without actually getting up a ladder and taking a proper look.
Would you hand over the cash ? What does the bugger do with it ? He does a runner of course.
As for the chimney, it's been pointed and the danger of imminent collapse was not reported. I've inspected it with binoculars and it looks solid. This is a classic example of FUD - Fear, Uncertainty, and Doubt; a well known marketing technique.
I should add that the bloke is white, stocky build, short dark hair and I'd say in his 30s. He has a mate with him in the van.