@irontoenail - People all over the world sell their hair, or even donate it for charities that make wigs for cancer victims.
If you are looking to get some hair extensions, I think the best advice is to find someone you trust, who has a lot of positive references and then just get the best deal you can afford. Most of the time, the quality is going to be reflected in the price. It's not necessary to know exactly what remy hair extensions are, or the difference between single drawn and double drawn.
All you have to know is that the more expensive it is, the better it will be. If you can afford the best, you should get the best. If you can't afford the best, then get what you can afford.