To buy WOW accounts is one way to bypass some of the lower less exciting levels of the game. Some players actually buy wow accounts to have an extra character to team up with their existing one.
When you buy a WOW account, you are buying an existing character including its skills, reputation, inventory, and more. This wow account have been created by either players who are no longer interested in playing WOW or by people who create accounts for profit.  Another option is to have these account sellers create a customized account to your specifications.
To buy WOW accounts gives you a chance to play another wow character class, usually at a higher level, and to save a great deal of time. You could save thousands of hours of play time by buying the account instead of leveling up. This saved time can then be used to play WOW with your new character at a higher and more changeling level.