Sorry to ask the obvious,the surface of the head needed cleanning up and that`s natural as they do many of these a day and fine grit paper on a glass surface is the best way.But as I have machined heads,brakes etc. myself,qualified boilermaker,and have done a bit of machining and fab work.Now for the machinist to get low spots,it would have to be low on one entire side,the feed slides or travel slides are faulty on milling machine or shaper,the vice wasn`t secured(then it would spit out and really damage it),or it moved in vice(see previous).The head would be checked on 3 parameters on set up,feed and travell calibrated on minimum 4 equally opposing points(also double checks level).Well what I`m trying to say is a few simple things,first did you remove head studs properly and in sequence,did you torque up head studs with equal pressure and in sequence rememberring to do it in stages.Not saying you didn`t just asking before I make the next observation as if you take it back to be rectified that`s what he will blame it on.Second do you know how much the cut was eg:0.025mm,0.050mm,0.075mm etc. Judging by the meat on the bowl lip of the head it looks rounded and it probably needs to go a bit deeper but I don`t know if he can and still leave a decent lip to aid gasket seal.The lip looks from the photo to have a somewhat rounded lip edge.Now the lengths of the studs might be a prob if they bottom after head work,check this by putting a small ball af alfoil around bottom of one stud,assemble and tighten stud down finger tight or just nipped.Take apart and see if foil was squashed by stud and how far.Your might need small equal shims under stud head.But what really caught my eye was,did you decarbonise the head,it looks like it`s been cleaned by an acid bath as no visible scuffs from buff.Are you sure he did actually machine it and not just wash it,the marks will still appear on surface when the gaskets completely removed,looks like he took your dough and just soaked it.Is the alloy any duller in sheen?and looking towards the rear bowl lip edge it looks a bit rounded,they need a good lip edge to seal and if he machined it,it would be a sharper edge from being taken down.Tell you what,print this out,take the head and this thread back to the shop,and ask to be refunded or problem rectified and if he wants my proffesionnal opinion he can contact me on
traceycoxmaitland@hotmail.com ,I really wasn`t having a go at you just explainning the process and what I perseive to be the problem and I hope it works out.