The best teacher of all is "experience" - by all means get the Razor Edge book but the problem is if you are going to make a business out of it you will need the right equipment - many of your customers will want 'speed of service' so you will need machinery of some description. Secondly, you will need to be able to sharpen everything you cant restrict yourself to knives. Scissors, chisels, secauters, shovels, spades the whole range of edged tools. The next thing is practice once you have the technical knowledge and equipment. Grab every edged tool you can lay your hands on and practice. Remember you will get custom from the average kitchen knife to the best of hunting knives and they will all want something different - even those who will ask for "not too sharp". If you believe you can't handle a job eg a $1000 pair of hairdressing scissors then don't do it refer them somewhere else - the last thing you want to do is get a reputation for a botched job. There are too many 'cowboys' who set themselves up with a grinder and profess to sharpen anything. Again practice is the important thing if you feel confident you will be able to do the job. I wish you luck in your venture.
