As Jon says, B18C5 is the USDM ITR designation. B18C-R is the JDM ITR designation. USDM ITR swaps are VERY hard to come by, so if you find one, there's a good chance it was stolen. JDM swaps are quite common, and usually cost about $4500+. My guess is it's either a stolen USDM swap, or he's just selling it that cheap to scam a quick buck and disappear. Also, from the pic, that looks like a 96 spec, so I doubt there's only 20k miles on it.