I generally report all scammers I get through e-mail, so my provider can block them. Generally, you can get their IP address from the e-mail header, and do a whois on it. I have found several heading back to some university computers to places like Africa, but the most from Croatia, or former communist block countries.
Now Gunbroker did charge me a $2 one time fee to validate my credit, and I've never had to pay anything else. There are many online businesses who do this. I've been with them now, while including changing my e-mail once, for about five or six years, and have never been asked for anything else.