[Zeke]

As a contractor (in the building sense) it is against the law for me to remove or alter anything I have done on site. That is listed in the CA Business and Professional Codes, but it does seem specific to contractors since it's in the part that governs the contracting business. It might suggest a precedent though.

I see a couple of choices. First, I wouldn't accept a partial payment without something in writing regarding the balance. You could offer to reduce the bill for immediate and full payment and be done with it, but I would not take only half. I'd start at 90% thinking as 85% as a goal and I'd negotiate a percent at a time to let them know 50 % is way, way out of the question.

Following those efforts, I'd send a certified letter demanding full payment in 30 days (typical legal demand maneuver). No payment, small claims. I've sat in small claims court and verbal contracts are honored. All you need to show the judge are dates, times, facts and any receipts for expenses. When the judge asks the defendant if any work was done and they say anything but no, it goes downhill for them from that point on.

Make sure you are addressing an individual, not an LLC, partnership or corp. They may try to brush you off if they have such an entity, but they won't have much in the way of individual defense without a contract with you. I can't be totally sure about the last part, but you do have to know whom you're dealing with.