Legal Question in Real Estate Law in California

If the person has assets or income (or may in the future), it may be time to sue them, or let them know you will.

That is what lawsuits are for. If the debt is under $7500, file in small claims court. If a lot more than that, you could hire an attorney to file in Superior Court, but first research whether the person has any money or assets. The cliche is that if they don't have any money, that is what you're going to collect. If you get serious about hiring counsel, feel free to contact me for the legal help you'll need.