In short, an annuity payment is the income of money that is withdrawn monthly from your invested annuity policy which has expand and compounded interest over a large period of time. A lot of people do not sell their annuity payments however, instead they use them as retirement income or to foot regular monthly expenses like medical bills and also home mortgage. So think about the long term affects to your financial situation if you want to sell your annuity.
When people purchase a structured settlement they are purchasing the monthly income from someone else in exchange for a lump sum now. Many people in tough times will go to a loan before they consider using their settlement or annuity income. The annuities will have gained value from their regular payments (made by the annuity holder) and the interest compounding. Many people do not know that they can sell their structured settlements or their annuity payments in exchange for a lump sum payment.
Even though when you invest in a settlement, it is intended to better secure your financial future and offer a stable income stream, but you can never be sure if they are sufficient for your individual financial needs. 
When you get the chance to build higher returns on the other hand, perhaps through a private business or other investment opportunity, you may need more capital for doing so and liquidating your annuity by selling the payments is a very likely option. As you start to evaluate the value of your annuity make sure you get a structured settlement quote from a variety of companies.
Beware that there will always be fake annuity buyers trying to prey on uninformed customers. If you are hesitant at the prices offered to purchase structured settlement, you should ask a financial expert to compute a reasonable market price for your annuity payment sales. They can also help you avoid selling your annuity payments to uncertain annuity buyers. Each structured settlement is issued frequently and the precise value of each settlement is stable and determined when you purchase structured settlement from the annuity broker.