On the Form 8867 (due Diligence) Part V   Q. 14  "Have you determined that the tax payer was unmarried or considered unmarried............." 

How would I (tax preparer) determine whether my client is unmarried? I can only ask if he/she is unmarried. Do I HAVE A proof that client is unmarried? No. 

So if I am wrong I could pay $500.00 fine.

I would be more comfortable if the question was " Did you ask the tax payer if he/she was single/unmarried.

Any thoughts?