It's the mistake of owner if CTR was going high then why did he not removed ads.
keep eye on CTR if it goes more then 1-3% then remove AdSense ads from site.
You mean dynamically? Stop showing AdSense ads when CTR goes above 3% and then after a few hours re-enable them?
Just keep eye on CTR if your daily CTR is around 4% then no. problem but if suddenly it goes up let say 10% or more then you should remove.
if your daily CTR is around 3% and if it fluctuate between 3-7% as per your experience then up to 7% CTR is ok.
so it varies case by case but for security download AdSense app from play store and chrome extension so you can keep checking your daily revenue . if you see a sudden big jump in revenue just start to worry and try to find the reasons of such big jump in revenue .