> Trust them to produce, and if they are not producing, let them go.
If you are firing someone for performance, you have done a performance review. It's just that it might be entirely in your head or based on office gossip about who appears most productive.
You wouldn't optimise a program without a profiler, so you shouldn't make hire/fire decisions on productivity without some means of measuring productivity. I know it's hard and tends to result in stupid metrics, but that doesn't mean it shouldn't be attempted.