The flat earth society is correct in surmising that all observations require the senses. Whether looking at tools, the sunset or a ship sinking on the sea, they are correct in that no observation can be made without the senses.
The problem comes when this is pushed too far.
If I become blind, the world and everything has become black. It would be a correct observation to say it must be black for everyone and this would be irrefutable.
Let's dial it back. If I have poor eyesight, then the world is actually a blurry mess. This is irrefutable again.
I know of no sense that is perfect - Humans can't smell bombs at an airport so bees are trained to do it. Most humans can't hear a dog whistle, it still makes noise to a dog.