Let me guess, you sold an expensive item on a 0 feedback account and even though you thought it was dodgy, you still sent it? Unfortunately, if that's the case, there's not really anything you can do about it. You could try calling eBay, but they are unlikely to do anything about it. They can't get your item back.
The only thing you may be able to do is if you sent with tracking, sign up to My Post (it's free) and try to intercept the parcel and get it redirected either back to your place, or a trusted friend (I'm not sure you can do a return to sender redirect, but you can redirect to a different address to what's on the label).
In future, block anyone from overseas buying expensive items. If the buyer is from Nigeria, or some other country want to post to their cousin in Nigeria, don't do it. Sadly, this is probably going to be an expensive lesson for you. The scammers target low feedback sellers selling expensive items, because they are an easy target, especially when they offer you more than the price listed.
One last thing, even though it's a Nigerian scammer, you can't name and shame here. The mods will remove the buyers ID and email address. EBay don't read these forums.
