Celebrity Muffler & Automotive Repair

I wish there was an option for VERY POOR. This is the worst place I have ever been to. I was having a problem with my Range Rover. I was in Los Feliz and stopped by a Land Rover mechanic. He told me that the problem was with my catalytic converter. It was damaged and needed to be replaced. I went to Celebrity Muffler because it was close by. The mechanic told me not to pay more than $300. Celebrity Muffler quoted me $600. I told them I would give them $300 cash. We agreed on $300 cash. A few hours later I came back. Picked up my car. Paid. And was on my way. Four months later I was doing a smog check -- I failed it. The reason? My catalytic converter was the wrong type for my car and on BACKWARDS and as a result causing further damage to my car. If anyone knows how I can sue these people let me know. I lost the receipt and have since sold the car. But anything I can do to spread the word about how AWFUL this place is I will.