I was actually refering to selling domains when i said "reselling", as in getting an account with enom and setting up a domain website where users can buy domains from me.
If you want to get into the actual business of buying domains and selling them on then yes, you simply use a site like
www.pool.com or
www.deleteddomains.com and buy the best expired domains or even reg up new ones to sell.
You can use tools like on
www.trafficrankers.com to check out stats for the sites, alexa, pagerank, google indexed pages etc. The more stats the more money.
Goto google and type in "link: domain.com" this will bring back all the indexed pages google has of that particular domain.
Then you would join a forum like namepros.com, dnforum.com and put your domains up for sale, domains with traffic sell no matter what they are and a decent domain will always sell for more than you paid! It's a good business really...it's just a case of hunting for decent domains.