We've had the same helper for more than two years. We found her through a friend who knew her and strongly recommended her. We hired her without meeting her, but we did speak to her on the phone.
We had interviewed about 6 people, but none of them seemed very confident. Our #1 priority was someone who would not only look after out baby, but play with them, and genuinely loved children: someone who could prioritise and make decisions - not need to be instructed over every last little detail. #2 priority was keeping bathrooms and kitchen clean, #3 was laundry and mess was a distant 4th. She's been wonderful since day 1. Were very lucky.
Perhaps my expectations were a little different - I was home with our son until he was nearly four months old. Even with some part time help (after a C section), I still found keeping everything running smoothly to be very tireing. So when something isn't 100% perfect, I remember that everyone is human, and we all get tired or sick or forgetful. Having said that, these times are very few and far between.
We've always had the approach that we won't stand over her - that she should have the autonomy to do things as she feels comfortable. Then, if there's a problem, we can discuss it. I think the autonomy and the respect we show her gives her the chance to be responsible, and she rises to thsi challenge every day.
We hope to keep her for as long as we need full time help in Hong Kong.