See my post Botters and Spoofers and Cheats! Oh My!
This is 100% the biggest issue in the game right now.
1) somehow get rid of all spoofing methods (unlikely),
2) rework the gyms system in some way that will help (underway I believe but I'm not holding my breath for any miracles)
3)introduce pvp to compensate somewhat for the gym flop.
4) invest swiftly and adequately in reporting, logging and identifying methods and banning these game ruining cheaters indiscriminately, only accepting account reinstatement if they have made a mistake and this can be appealed and proven.
I have reported many, many times but nothing. Same spoofers still at it with more an more accounts.
No prizes for guessing which team of spoofers has infested my town and city
Something has to be done as the game will flop if the GPS spoofers keep increasing at the rate they are.