Visible cracks. It's a good idea to pull the seal off and stretch it.
If any rubber is left on the bottle when you open it.
Visible indentation that does relax out in a few minutes.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk