I had a similar experience.
The guy came highly recommended on the Neighborhood app.
He 'wallpapered' a downstairs toilet for me and he'd actually torn the paper into strips with raw edges and laid them on top of each other. He hadn't pattern matched where it would have been possible to, the full width wallpaper runs were either too close together or ever so slightly too far apart but not a single one was perfectly pushed together, and there were huge blobs of wallpaper paste dobbed all over, added to which he'd climbed onto my toilet seat to get access to the corner and when I said to him you've broken my toilet seat he said no I never stood on it - when it was fine when I left for work in the morning and broken when I got back.
Whilst he'd done a much better job in the living room it still wasn't perfect there was no pattern matching around the corners and he'd actually gouged into the ceiling where he was cutting the paper with his Stanley blade.
In the end I told him he'd have to refund me for all the wallpaper because it was all absolutely ruined, the whole lot of it, which you did he paid up over £400 that day and he said "I don't know what went wrong I've never done such a bad job"! No sh*t!
The worst thing was that for the paper in the downstairs toilet you actually can't get it any more - it wasn't anything expensive or super special but I really really liked it and he wasted about the only supply that was left in the UK and I was absolutely gutted.
It's easily been 2 years now and I just haven't had the mental strength to go and try and find somebody else to do it 🤣!