I have bought and sold over 800 knives and with each purchase or sale learn something. I ask a lot of questions and make myself available to answer questions posed to me. Custom knives are stolen and resold. A dealer can usually provide instant product including knives from makers with long waiting periods. Expect to pay a slight markup.
Books are an excellent source of information.
Read Ken Warner's Knives Annuals, Bernard Levine's Guides and any cutlery related articles, magazines, etc. that you can get your hands on. Try to specialize as opposed to buying everything that catches your eye. If you want it badly enough, you will find a way to afford it.