You will pay about double in gold to the sites than you would have to selling to a private buyer. You will get scammed a few times through trade chat but it is well worth it to find a steady buyer or two. Best bet for the casual gold seller is to buy something a little easier to control first. I advertise to buy things such as steam games etc, having them send to me first. I then expand to paypal donations or game time codes. Build a relationship with some of these people and they will continue to buy from you. Best thing to do is never screw someone. I sell my gold for 1k=$1 better prices than the gold sites. I have 3 people right now that pretty well take all the gold that I make from botting two accounts 8 hours a day. They always tell me that it is nice to buy from someone trustworthy.
TL;DR
30days=15k once you establish a buyer