Legal Question in Civil Litigation in California

Re: cashed a check

Do you have anything to worry about? Yes -- you are going to lose this lawsuit and are going to have to pay not only the $450, but also interest and court costs as well as any additional expenses the mother reasonably and foreseeably incurred as a result of your actions. If she was hit with bank charges for bouncing checks, or if she was assessed late fees by creditors whose payments did not go through because of insufficient funds, you are going to have to pay those charges along with interest thereon.

Oral contracts are legally binding, and you made an oral contract not to cash the check. Your ex-roommate's mother is not at fault "for not canceling the check", since you had contracted with her not to cash it. Your promise not to cash the check justifies her decision not to pay her bank to cancel it. Equitable principles also come into play here, and the court probably will not allow you to even argue that she should have acted as if you had not made this promise to her.

Your roommate's mother wrote this check in order to pay the rent for a particular month and only under particular circumstances. She had agreed to pay one particular debt that her daughter owed at the time, and not to become generally responsible for any additional debts that might arise in the future. You accepted the check subject to those conditions, and had no right to use it to pay a different debt that your roommate later incurred.

(Imagine if, instead of giving you a check, the mother had left $450 in cash for you to use under the same conditions, and that you later agreed not to keep it. Do you think you would be entitled to take it later anyway just because the daughter incurred a new debt that her mother had never agreed to pay? There is no meaningful distinction between these two situations.)

It is also theoretically possible that you will have to pay punitive damages, though I doubt that this will happen in such a small case.

You might want to reach some sort of settlement agreement with the mother so that you can avoid going to court and having a judgment entered against you. You may even be able to negotiate a lower amount than what she is seeking. But going to court strikes me as a bad idea since the law, the facts, and the equities all seem to be on her side.