I've been cleaning leather for the last couple of years, did the Extracta course which taught me the basics of the types of leather and cleaning process (singular)
After encountering the odd problem along the way, I decided further knowledge was required and I have therefore just spent two VERY WORTHWHILE days last month with Andy and Judy at Harrogate. Not only are they very nice people, they are also very knowledgable and willing to impart that knowledge on to anyone who is interested, for a small fee of course!!
Expect to fork out around £1000 for the course and getting set up with what you need.
Without a doubt the best short course I have been on for a very long time, there is a hell of a lot to take in and even more to worry about afterwards!!
Did two leather suites today and got another lined up for tomorrow, also got a full aniline recolour lined up for the end of the month. It is harder work than doing material suites and the risks of f**king up are far greater. However, charge accordingly, I'm not going to give you a price as prices vary greatly from area to area and from person to person, but as a rule of thumb charge around 1.5 times what you charge for fabric suites. I find the time it takes to clean is roughly the same as fabric.