Dealing with lads looking to pressure wash my parents roof?

Since last November I have one particular chap adamant to get up on the roof of my parents house and pressure wash the tiles, somewhat mossy but not that bad. I wouldn’t mind if I had the money to pay for them (charging 600 euro for a bungalow roof), however I would be concerned that the tiles may give or they would end up having a leak.

The thing is he has called recently this week, not once but twice, first my mother then looked to chat with my father. A few others on the road had the their roofs done, but I feel that this chap isn’t legit and not insured. I maybe too cagey with this but then again I’m not taking any chances, considering he has called multiple times now.

Located in the south Kilkenny/waterford area if anyone else is in the same situation.