I only have the Red Book
20% dealer margin seems to be very slim to my way of thinking, unless there is a good dealer prospect of immediate turnover.
I am a price cherry picker, and strictly a collector,
but I look for more like a 50 % margin, although I don't always achieve that. (Sometimes achieve much
I do however, look for bargains across the whole of numismatics, not just U.S. coins. The much wider numismatic horizon makes it far easier to find coins for my collection at opportunistic prices. Decades of experience helps.