There's this deceased prince in Nigeria who cannot release his funds...
etc etc
The world/internet/emails are full of scammers with new ideas every day. Don't feel too bad, you're not the first to be drawn in to something which sounds potentially good. But honestly, if it's too good to be true it always is.
If someone is truly interested in a domain name (or anything you are selling) then they're willing to do it properly, and that means they pay you, and
never you fork out something up front. You hold the item they want, so why should you pay
Your domain name (sorry) is not worth very much as there are many alternatives, especially without a hyphen, and it's carries a potential for trademark infringement which means domainers with decent money to spend wouldn't touch it. So in this case the deal was unlikely to be anything but dodgy.
As with any problem in life, just learn from it
do a lot of reading round the forums, see what sells and for what, as well as namebio.com, DNJournal.com and domain sherpa etc. Buy low at first, and things with obvious commercial value like "ShoesOnline.com" (that is taken of course, just an example). And stay away from anything but .com until you know what
really makes a good domain name.
Before you buy another domain (especially non.com) do some investigating on namebio to see similar sales (and make sure they are
similar). And expect to potentially take months possibly years for it to sell (quick flips come with knowledge and experience, it's not hard, but you need to read and have a decent domain name)