All depends on if they need to use scaffolding or not, if they are following the rules they won’t do it off roof ladders as if they fall they won’t get shit from there insurance.
However 4K seems a lot as I got my 5 bed house re-roofed for around 6K (excluding scaffolding)
I had a 3 bed detatched house which we had a few loose slates on, got those fixed, all the ridge tiles reseated and mortered along with the retaining rods then plastic facias and new guttering for £650. They were a bit rough and ready to look at but did a good job.
That is very very cheap, for new facias, guttering and ridge tiles. Did they have irish accents by any chance.
If you have a slate roof you need to be careful as if you break any of the edge tiles (this is much more of a risk if your roof is built using spanish rather than welsh slate as its thinner), they can have to end up taking nearly all of the tiles off to the replace them as removing the copper nails is a bastard. Which would make your initial quote seem cheap