I am a Field supervisor in my market, so I get a small salary and get to run a route so I do pretty good at the end of most weeks. I try to do as many QC's as possible and the way I get paid there is $6 for a QC and $5 to fix any minor and $10 for any major infraction, up to the total of what the job paid the tech. I am not going to charge them more than they billed but I will charge them back for the entire job to get a point across. I rarely have to do this, usually it is a minor infraction so I end up with $11 at the most for the QC. I do go face to face with the techs and show them pictures of their mistakes so that they will not continue to make these same mistakes and I do let them know what they are being charged for.
With you not being 1099 I don't think you can charge them back but $10 to $15 a QC is a fair rate since you are usually looking at no more than 15 minutes of work / walkthrough of someone's work.