One of the great benefits playing a MUD back in the day gave me was the ability to negotiate a lot when trading stuff, so I got a feel for when to push, when to take the offer, when a negotiation just wasn't working out, etc etc. That said, this book has about 90% of everything you need to know.

I don't really like self-help/improvement books and the like, but this was just no-nonsense and straight to the point.