Ranting About the Nightmare Client Who Won't Pay for Trane AC Service Call

Had this client call me out for a Trane XR16 that's been acting up, superheat way off and won't cycle right. Quoted her $450 to diagnose and recharge with R-410a, but after I fix it she claims it was 'just low on freon' from normal use and refuses to pay the full bill. Watched a Bryan Orr video on handling deadbeats like this, but damn, it's still a hassle chasing the check. Now I'm out the time and gas.

What'd you end up doing to collect that $450? Ever had to file a small claims on a similar job?