Benefits of selling the mobile phone online as compared to offline mobile store?

If you sell it in a real store you are sure to get your money in cash and immediately

When you sell your phone online, you're generally going to get more money for it when compared to selling it/trading it in at a offline mobile store.
This is because the offline mobile store needs to make a profit from reselling the phone you sell them; unlike buyers online which usually want to buy your phone to use themselves.