Domain names once purchased have to be renewed after a certain period of time to keep them under your ownership; else they are sent back to “available” pool of domains and can be taken by someone else. The major cause of domain getting expired is simply because the owner forgets to renew it. There are, however other reasons too.
Sometimes the business under that domain name is no longer operational and therefore the domain is simply abandoned so that a new domain name can be purchased. So should you purchase a used domain name or go with a new one. Well here are some pros and cons which might help you decide :
1. The domain is already listed in search engines
2. It already has a good page ranking in search engines
3. It was a part of link exchange
1. It was previously used as a spam target
2. It could be banned in some regions
3. It could have history of robot attacks and DDOS attacks
Things to be careful about once you buy a domain:
1. Be aware of the expiration date
2. Make sure the email address for correspondence is valid and working
3. It helps if your domain registrar has good customer support.