What on Earth should we be doing, then? You should accept that the process is going to cost you, and that there are going to be both false positives and false

What on Earth should we be doing, then? You should accept that the process is going to cost you, and that there are going to be both false positives and false negatives. Trial periods solve false positives, and you eat the cost of onboarding someone and their 1st 3 months or whatever. It sucks, but make the decision and move on. If you have this happen multiple times, your interview process isn't rigorous enough. To improve false negatives you need a mix of inputs in your interview process. One way to get this is long/multistaged interview, but you will lose people this way too. Accept that if you are asking an interviewee to do real work (e.g. real world code) independently you should pay them for the time, and know that you'll lose some good candidates if you ask.