Selling On Line Fail

So recently, I decided to give selling on Amazon a chance. I found an item that I could flip for a $30 gain. That's awesome, except I did not know what I was doing. It spent every bit of my profit on shipping and then I came to realize that I selected the wrong picture and needed to include a car. I had to buy the car on amazon and have it shipped to the buyer. I actually lost money on the deal. However, I have been talking to people who do this for a living and have learned a few things. Had I known then what I know now, I would have turned a nice profit. I will be trying this again and plan to make money on it this time.

Have you ever tried selling online? What are some of your favorite items to sell?