Pinnerite presented the following explanation :
Three scammers offered to re-mortar the edges of my roof tiles for a
reasonable sum.

While they were up there they lifted a ridge tile claiming the whole lot
were now loose and for a large sum would be prepared to redo them.
I declined, paid what had been agreed an they left.

My sympathies. I see off any itinerants suggesting I might need work
doing. I use a local guy who works alone and I see doing lots of work
in the area. For cost ideas... Its a semi and last year I had him redo
the ridge tiles on my side and the adjoining semi, for £80 each.

A few months before, I had him reflaunch the chimney, which had
suffered a small amount of ingress for a few years - that cost £60.

Last week I had him attend to some 20 foot of flaunching along the edge
of some tiles, down from the ridge. We were getting some ingress to the
bathroom ceiling, for the first time, following the 'beast from the
east' rather unusually - blowing weather at the building from the east.
That cost £60..