1) I'd take my least precious guitar for my first "setup" from a "luthier" I don't knowWhat would you do ?
2) In your situation I'd (have) paid the price asked, NOT let the same person make the adjustments, then I'd order 50 bone nut blanks off the internet, so I'd have 49 backups if I screwed up the first one
3) When I have the new nut as close as I can get it to the way I want it, I'd start again looking for a competent and reliable tech (I myself am not competent or reliable)