As the saying goes, good help is hard to find. More specifically, reliable help is hard to find. In most cases, you'll be hiring younger people, which means you will eventually come across those that don't show up on time, etc.
Interview is a simple 5 minute process. You arne't interviewing for VP of a large corporation. You're interviewing for a simple basic labourer. I'm not trying to belittle our chosen business ventures, but let's be honest, for an emplyee, detailing is a very simple labour job, similar to shoveling snow or moving furniture. What you're looking for in the interview is a sense of the potential employee's ethics and personality.
Hourly pay is basically the only way to go, unless you have something very specific in mind (and you have a very specific detailing business, like wholesale-only where you have an assembly line type of detail shop).
Keeping up quality is essential, as your employees could literally put you out of business if you aren't careful. The answer to this one, which is one of the most important, is surprisingly simple. Keep your eyes open. Many business owners work hard in the beginning, get the business running and profitable, hire a bunch of employees and then walk away, showing up for a few minutes a day just to collect the cash outs. You can't just do this. Either you hire a manager (which is going to be a much higher salary than your employees), or you have to be there, at least some of the time. Personally, I check EVERY vehicle before it leaves the shop. I also constantly check on the employees as they're working, and point out anything they're doing wrong / I'd like to to see done differently.
Again, we're not talking about employees that make $75,000 yearly. Your employees will be happy with their pay cheque, and if they aren't, they will quit. At this pay grade, the types of employees you're going to get aren't the life-long loyal bunch, and you can't expect that. If you find yourself in a revolving door, well, that's just how it can be sometimes.