As someone who uses a spoofer app for Pokemon Go, the anti-spoofing is pretty limited.

There is a "you can't go 500 miles in 10 seconds" style check, that checks your displacement against your previous position periodically to makes sure it's realistic,

something that makes sure your GPS is always drifting a little, like a normal phone GPS would report (which the spoofer app builds in),

and other little things such as if it has camera permissions and you take a photo in game, the location in the photo metadata matches your in game location.

I usually play in my house in the North of England and regularly spoof the app to be in London, New York, Paris Mall or Tokyo.