There's a couple of ways to tell for sure, real from fake. Just looking at it won't always tell you, some of these KIRFs are quite convincing now.
Look at the kernel version, if you see "KST" (Korea Standard Time) in the string, that's legit. On the other hand if it's "CST" (China Standard Time) or nothing at all, that's a KIRF. Another way is Antutu, that will definitely tell you what you've got.
If it's coming from Ebay, counterfeits are not the only risks. There's blacklisted IMEIs as well, when phones are reported stolen or missing.