Cashing an on-us check is final payment. Cashing a check drawn on another bank is simply an accommodation, and you can pursue the person who negotiated it to you. That creates an obligation. If your state law permits offset in such a situation, go for it. If not, perhaps you'll need to use other collection methods, such as small claims court.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8