Today is all about deciding whether or not you want to continue with your niche or not. It’s a pretty simple decision, if you have achieved good rankings, i.e. in the top 5 and you are not getting traffic then it’s time to go back to the drawing board. Ed makes a very good point and that is not to be discouraged by a niche that hasn’t worked out just think of it as a step closer to the one that will. The more you go through the process the better you will get at locating profitable niches.
If you are getting traffic and not making any sales then again it is time to go back to the drawing board. I would look at reasons why I am not making any sales and try a few things first before giving up on that particular niche. At least one sale for every two to three hundred visitors is something you should aim for.