At work I use upol easy sand , followed by a thin skim of upol dolphin glaze as a stopper then 3M glazing putty to get most of the scratches and pinholes.there are 2 types I use, red for large areas if pinholes are few and far between and green if pinholes are more of a problem .
even then a few may remain after highbuild primer, if so then apply some 3M glazing putty to the pinhole and wet sand down.
Stoppers and glazing putty needs to be applied as thinly as possible, use the easy sand to achieve the shape.
pinholes tend to occur when the filler doesn't flow when being applied, Thick fillers like the easy sand drag as its dense.that's why a wet ,nice flowing stopper such as dolphin glaze needs to be used on finishing.
after the primer has dried go over it with a bright torch and look closely for pinholes, apply the putty before sanding the primer.
Even after 13 years of applying the stuff i still get issues with pinholes but you just have to check closely before you put colour on top.