If the customer modifies or uses the device in a manner different than what I set it up for, could I still be liable?
people go to law school and get degrees just to debate issues like that .
in a situation like this if a employee feels their privacy is invaded and sues , you may be included at which point liability isn't the issue but the cost to defend yourself can far outweigh the profits on the job
the chances of legal problems from covert recordings is far greater than MOH violation in my opinion
things like the push to talk button or disclaimers for the customer to sign just show that your aware of the issues