Speaking of MI’s - Unless you are familiar with the Coal Layout - DO NOT start if you don’t have them and cannot download them. Don’t rely on a before photo as the chances are that they are on wrongly.
If the coal base has peaks upon which you place the coals, be VERY aware that they are fragile. If you do the natural thing and grasp a peak to lift it almost certainly will break, and they can be 3 figures to replace.
Inspect everything carefully and point out any cracks etc to the punter and take photos - you do not want to get landed with “it was okay before...,,,,,,”
I always had punters sign my T&C’s which clearly said, and I had pointed out on the phone, that even if I have to cap off the fire the service charge stands. And that return visits will be chargeable - the flue may have a birds nest for example