Before registering a domain, have a look on dnsaleprice.com to see how many domains have been sold for that keyword. If like Sedan, there are only a couple of sales in .com and they are for $135 and $250, you won't be able to sell it in any alternative extension. Another tip is to check Sedo.com and see how many people have bid for domains with a particular keyword. For Sedan, the .mobi is priced at $7,500 and the .us is priced at $10,000 but there are no bids for any domain with the keyword Sedan in. The owners of Sedan.us and Sedan.mobi have little chance of selling, the owner of the Sedan.pro has no chance of selling. When you register a domain in any alternative extension, it's got to be so desirable and valuable in .com, that like champagne being poured into a pyramid of glasses, the champagne or keyword demand in the top .com glass spills over into the other alternative extension glasses. If you are new to domaining registering alternative extensions like .pro is like going for a walk in the desert without water. It's best to start buying .coms on a forum for low to mid $XX and see if you can sell one for $XXX. That way you get a feel for what works and what doesn't.