Okay, here the deal with confidence. - You can't have enough confidence as a measuring value unless you don't know the timeline in which you will be able to sell the domain name, at whatever prices. Unless you are buying a name to start your own company, you must know the time frame in which to sell the name. You must narrow down possible buyers who will buy your name. The registering and waiting game is a bad bad strategy.
If you are new in the business, you won't know enough to be able to register new names and then anticipate selling them for unrealistic prices. Most of your money will go down the drain.
Visit sites like Namejet, Godaddy auctions, Flippa and buy established names with some type of traffic, pagerank and back-links.
Domainers live in an insular world. They create their own fantasy universe in which they seem to own the best names with crazy valuations.
If a newbie has priced a certain name in the portfolio for $1000, let's assume. They should then offer it for $25, just to see if there are any takers. If none, then, they will know what they are doing wrong.