Let's say you come up with a great idea for a domain name, you go to godaddy and buy it, after this how do you find out if anyone else ever tradmarked or copyrighted that exact name, maybe they did not buy the domain name maybe it expired etc. For example, lets say you thought of the name superfrogtoys.. you bought the domain name, and are about to make the site. Only to find out down the road someone has already tradmarked or copyrighted the name superfrogtoys.
The best way that I know of would be a trademark search. There's a lot of rules and regulations about trademarks and how things are dealt with depends on where you're located. For example, many companies will trademark a name but depending on how they did it or the local laws it may only be enforceable in their general operating area or potential area. So if you have a used tired store in Vancouver, Canada with a trademarked name then it may be hard to enforce that trademark in China on a .cn domain name. I've seen trademark searches in the US for $450. There may be a cheaper alternative though. Another way would be to do some of your own research on the name. You can get a lot of information off the net on corporations that would be using said name.