An account that has a huge following paints a picture of credibility to potential followers at just the first sight. Naturally, no one wants to follow an account with fewer people because it is deemed fake even if it is genuine with great content. It is this role of massive numbers that have led many people to buy free followers. Some buy few followers to make the account look active and act as a foundation to attract potential ones while others purchase a lot more. Yes, it is a great way but you likely to lose reputation and integrity if your followers notice the trend of your account.
It may be a sign of low self-esteem because you are trying to be popular yet you not. If a person followed you when you had five hundred followers and the next day you at ten thousand, automatically it will raise questions about your authenticity. Though they may not know that you purchased these free followers, the sharp increase puts your integrity at stake and you likely to lose such genuine followers at a faster rate.