Perhaps the reason that you have not one but many clients who, like their employers, want to avoid payroll and Social Security taxes is that you have built a reputation as someone who will let them get away with what other preparers refuse to deal with.  There are two consequences of this:

1)  Bad clients drive away good clients.  It's better to develop a reputation as a preparer for taxpayers who want to be honest.  You can do only so many returns.  Why cater to those who don't follow rules?

2)  Eventually your reputation among clients will become your reputation at IRS.  Don't be surprised if they run a "preparer project" and audit every return you file.