If I recall correctly, the hub that comes on the Pista is not a flip-flop, it's a track style hub with provision for a lockring. You can however thread on a bmx style freewheel and it'll be fine. If the threads stand up to riding fixed they'll be fine with the freewheel. The issues will be:
a) The standard hub sucks.
b) Getting the lockring and cog off can be hard. If you don't have the tools/experience, have the LBS take care of it.
c) You'll have no back brake unless you run it fixed.
The price is quite fair if it really is in a good condition. I love the look of that bike and I love riding it, fixed with a front brake. I don't however really see me doing my commute on a fixed gear, but if you have a flat commute with decent conditions I'm sure it's a blast.