Im sorry to hear about your troubles here my friend..
Its never good to feel like that and have a rip off occur. I hope that the package does show up at your door tomorrow just so you don't have to go through the whole claim process.
How did you pay him? Hopefully Paypal so it is easies to get your money back
I would suggest buying items from members off of the forums here. Most of the time other members will help weed out scams and admins also help with that. Thanks Trips and AK!
I know there are plenty of FI exhaust systems that go for sale on this forum.
Hope that everything works out