Before you bought any domain, you should check the domain history whether it is dropped before or not. What is a dropped domain anyway? A dropped domain is a domain name that was previously registered but was not renewed by the domain owner. There are several reason for this. The owner might forgot to renew the domain name or the previous domain owner did not want to renew the domain. If the domain is banned, the previous owner might not want to renew it. He might used it for spamming. If the domain has been banned, the search engines will not list your website and you will not get any or little traffic from Search Engine.
Before you buy you can check it’s history at the Internet Archives’ Wayback Machine. Type in the domain, and you can check if it has been previously dropped. You can also find the age of a domain there.