First - Learn to identify ALL the types very well. It's easy and common to lose your a-- buying catalytic converters. Second - Be prepared to pay high for them with very low profit margin. Everybody is buying catalytic converters which makes it very competitive. Throw in core buyers who travel all over the country offering more than you'd get at the scrap yard and there's not much left. I lost EVERY repair shop I had been buying cats to a core buyer that came up from Boston area (three hours away).