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My reasoning is that a lot of people who are searching for their business domain name don't know much about buying domains. So, instead of looking things up in the WHOIS database - they simply type a domain name in the browser window and see "if it's taken".
What do you think?
If you have domains that get traffic, why not park them? Selling and parking are not mutually exclusive and you might make enough money to cover your registration fees.
Some like Sedo's basic service only provide unique visitors while others like Fabulous and Parked can also provide traffic analysis to show search queries and countries your traffic is coming from. You will want to look around at the various parking providers and evaluate the one who will work best for your situation.