It is becoming increasingly common to be able to sell Bitcoin from the same places that allow the cryptocurrency’s purchase. The main exception is currently Bitcoin ATMs, some of these allow you to sell Bitcoin but not all. If you wish to locate one, it is possible to do so using Coinatmradar.
All exchanges allow to both buy and sell Bitcoin. Choosing the right exchange to use when selling Bitcoin is a matter of identifying what kind of holder you are. The choices are a trader, a small investor or an institutional holder. This is because there are certain platforms like GDAX that are intended to handle larger orders that come from traders or institutional investors.
For retail clients that use the cryptocurrency, exchanges like Bitstamp, Coinbase, Poloniex or similar are better suited. Each one of these has its own user interface and some also offer other related services. Different exchanges have different levels of security with some requiring verified identification on any trade while others only require it for larger sums.
It is always possible to choose to exchange Bitcoin for a different cryptocurrency instead of cash. There are certain exchanges that cater to this service allowing for easy exchanges between cryptocurrencies.
There is also the option to make a direct sale. Certain platforms like BitQuick, BitBargain, LocalBitcoin and Bittlylicious allow their users to register as sellers. This allows them to be contacted by other users who like their asking prices.
Transactions are most often performed using either deposits or direct transfers to your bank account. After the transaction, you will need to transfer the Bitcoin to the correct address.
There is always the option to send Bitcoin to friends or family who have a Bitcoin wallet. Simply send it to them and pick up cash or another form of payment later.
(Note: As a safety precaution you should never agree to meet a stranger in person to facilitate any kind of exchange.)
{Note: While certain businesses are mentioned these are not the only options and should not be treated as recommendations.)