Hi! I'm new, so please forgive my technological incompetence!

I run a home-based business and sell some things on the internet. Lately, I've been getting many emails from different free accounts (yahoo, hotmail, gmail, etc) saying they are interested in what I'm selling but then they never follow through with the purchase or respond to any of my replies. I'm thinking someone (and I have an idea who...) is setting up these email accounts and sending me these offers as a prank. This person has way too much time on her hands and is just flooding my inbox with bogus emails. I know she's doing it from one computer and through the same ISP. Is there anyway to find out the IP addresses from these different emails I'm getting?

I don't care to find out who's behind the IP, I just want to see if they are coming from the same one so I can tell the difference between real offers and those that come from the same computer. I don't know how to find an IP out at all, so I'd need pretty detailed instructions (click this, look here). Any help you could give would be greatly appreciated! And if it's completely hopeless and there's no way to find out- Sorry, I just don't really know about it!