I tried to IM you to save posting this in your ad thread. But since you are not accepting IM's:
Is it the USG, or the IOM? according to FiveSevenForum, it can't be both a USG and an IOM. Does it have the round trigger guard or square? If its round, it could be the IOM or the TACTICAL, but if it has a square trigger guard it can only be the USG.
Five-seveN IOM (Individual Officer's Mdl)
The IOM variant is similiar in its basic design to the earlier Tactical variant, but differs in having an M1913 accessory rail, lined trigger-guard front strap, magazine disconnect ("magazine safety"), and taller, adjustable sights. It is single action, similar to the earlier Tactical variant.
It sounds like a good deal either way.
Five-seveN USG (United States Govt)
The most recent version. The USG keeps the features incorporated in the IOM, such as the magazine disconnect ("magazine safety"), single action trigger, and tall adjustable sights, but has some differences. These include a square (i.e. conventionally shaped) trigger-guard, tightly checkered grip pattern, and a larger, reversible magazine release. There has been some confusion between the IOM/USG. Just remember once again that no matter what your user's documents call your Five-seveN, if it has the square trigger guard it is a USG. According to FN, the name mixup is due to the transition between the IOM and USG versions, and USG pistols labeled "IOM" or "IOM USG" aren't any different than USG's labeled "USG".