You can just trust IP geo databases to be accurate down to the country* - and that's only most of them time and not even considering VPNs exist.

Sure, if something looks fishy you could then go through the appropriate legal channels to get a more exact location from the ISP, but false positives are going to happen so often, eventually everyone involved might get a bit cranky.

* Only the likes of Google have the scale and requisite information to keep more accurate and up-to-date databases, and even those are fallible.