1. Is your client a US Citizen?

2. Is the income from outside the US?

There are two possible criteria to exclude foreign income "bona fide resident" is one of them. The other is physical presence. 

Something like this might be helpful and you get come CPE for only $10 (or wait until next month and get it free) https://www.cpaacademy.org/self_study_show/a0D2S00000jUR7IUAW