5. In real-life detection tasks, is it better to be a "naysayer" or a "yea-sayer"?

What will be an ideal response?

Neither; it depends on the consequences of a "miss" or a "false alarm." Suppose that you are in the shower and you're not sure whether your phone is ringing in the other room. You might want to be a yea-sayer if you are expecting a call about a job interview, but a naysayer if you're not expecting any calls and don't want to get out dripping wet for nothing.