Those are exactly my thoughts and this guy has hundreds of positive reviews on checkatrade and is trading standards trusted trader approved.
I think I've been had. Fortunately, I haven't paid yet and won't be until he fixes it but redoing the whole ridge with the correct tiles correctly spaced, so he'll have to lift the fabric on the roof tiles too and put new stuff on as the screw holes will now be in the wrong place.
He told me it was normal to see daylight through the gaps between the ridge tiles. I started smelling something....