Did you pay by credit card - if so ask for the charge be reversed.
I would have done but I paid cash
If it's powdercoat i'm not sure nitromoors will remove it. the bb needs cleaning with a tap really. The brake boss- cut around with an stanley knife and dress with a file/emery paper as best you can - loks a bit pants on the boss/stay braze on it's self tough.
The stem appears to have the remnants of powdercoat from where they may have hung it up via the clamp bolt hole. more so the fact the inside of the bar clamp its self meaning bars will be a PITA to fit.
I can put some emery cloth on some dowel wood and remove most of the paint on the inside of the stem I reckon. You are right, the paint in the clamp looks like it's from a blanking bolt or something, I should be ok to cut the lump bit off, the rest should be ok there as it wont be clamped tight enough to come together if that makes sense.
I have nitromors, emery cloth and patience, I think I will try on the paint that is easiest to remove (i.e. on the bottom of the stem (not in the pictures)) and see how that goes about removing the paint and go from there.
You live and learn.