how many clicks and how long have you been running the PPC, these things take time. Sometimes people buy days after the original click.
On the other hand, you want to make sure you are converting as many of your clicks into sales as possible. So if you have been running it for at least a week and haven't gotten sales but are running up a PPC bill. You need to identify why people aren't buying yours vs your competitors. Is it the price? Is it your listing? is it your pictures?
Your goal should be to make it so that someone would buy your product over all your competitors. ONce you have accomplished that, THEN you run PPC to get people to your listing.
People sometime make the mistake that runnign PPC will magically get you sales..the key here is conversion. on a new launch, you need most people that get to your listing to buy it. Chances are when you first launch your price might have to be at or near cost.