Master rug is probably the most thorough... and takes a lot of time compared to more abbreviated training. Still, most training teaches you some observational skills, and learning to identify construction and test dyes is the most important part of rug cleaning. It will take years of taking classes and making mistakes to get good, so pay attention to the rugs you're most likely to buy and avoid them until you're doing enough volume to eat the replacement cost of rug now and then.