You pretty much just plug the IP into a geolocating API and hope. There's nothing else to do. Any collateral damage is on the legislation, not any individual site or admin.
As you say, IP geolocation is unreliable. Unfortunately that's the only option. If it is technologically impossible to comply with the law, you just gotta do the best you can. If someone in MI gets a weird IP, there's absolutely nothing any third party can do. That's on the ISP for not allocating an appropriate IP or the legislators for being morons.
As you say, IP geolocation is unreliable. Unfortunately that's the only option. If it is technologically impossible to comply with the law, you just gotta do the best you can. If someone in MI gets a weird IP, there's absolutely nothing any third party can do. That's on the ISP for not allocating an appropriate IP or the legislators for being morons.