I generally like to base my interview questions on the candidate's resume, asking questions of various levels of difficulty about the areas they claim to be skilled. I find it gives a better sense of their abilities than strictly asking about the tools/languages/algorithms being used on the hiring project. As such, each interview was already unique to an extent - and I might have noticed something like a person whiffing the easy questions but then getting an advanced one that didn't add up.

Also, the "architect" I inherited on the team seemed totally incompetent in a variety of ways, and insisted on using a fixed set of questions without deviation. To He kept flagging people through who seemed totally inept when I'd dive into their background, so they was also probably a tip off that they figured him out.