You've been doing this 5 years, they are asking for rechecks on 10-12 items every month, and they continue to give you the work? This tells me that either you are doing them too cheaply to begin with and they are ok with 10-12 mistakes per month or they are not mistakes, it's just them getting extra work out of you without paying additional compensation.
Either way I would ask for more. They can either get someone who doesn't make "mistakes" or pay me for the work I'm doing.
There are reasons that a body stays in motion
At the moment only demons come to mind