I can understand and sympathize with the employers problem when an employee leaves shortly after starting. Its difficult to flush out a benefit from high turnover, particularily if you feel that you've "invested" a great deal of time/money/effort in developing the new employee. Of course this requires a bit of a caveat..if your input consists of a checkout flight paid for by the prospective CFI, a five minute speil about how the last CFI "screwed over" the school so now the pay is $9/hr for the first six months and handing them a I9 forms to fill out so they can pay thier own taxes then it seems a bit misplaced to expect much loyalty whatsoever.
I've seen more flight school owners than not display a sense of entitlement over employees labor based on the idea that they are "allowing" the instructor to build hours.
The most confusing to me however how many times Ive heard echoed the tale of the instructor who stuck around. He didn't cut and run at the first job offer that popped up on Findapilot. He was there even on bad weather days. He filled in at dispatch, put together a ground school package, brought in new students. His experience has saved your butt, a student, an airframe more than once. He can't even remember all the other instructors who have come and gone but he knows every student, even the ones he's never flown with. Being a "senior instructor" hasn't brought much of a pay raise, if at all. Maybe he even accepted a pay decrease! but by now you've given him the access code to the office copier, trust him to drive your car to be detailed and once you bought pizza for lunch. He (or she of course) has been an all around professional and acted at all times under the notion that your sucess and his are intertwined.
A year and a half later he asks if you would write a recommendation or you hear about an interview he is hoping to get. He has given his all and really hasn't asked for much before. You fire him that afternoon and on the drive home you are already practicing what you'll tell the next interviewee about how important pilot development is to you and how much you want to see them succeed.
There are bad apples on both sides of the fence. I've seen more than one former instructor screw over the owner of my flight school, who I consider to be a great guy. For instance, the owner put one guy on a base salary of $10,000/year, with an hourly rate of $10/hour on top of that. Sounds like decent deal, right? Know what the instructor did? Worked about half as hard as he used to, including taking three weeks off in a row. My boss paid him about $3,000 for doing practically nothing.
Another instructor was hired to fly for a charter company. Before leaving, he screwed up the paperwork on--get this--*three* customers' 8710 checkride forms simply because he didn't care anymore. He didn't care that he was ripping off customers or tarnishing the school's reputation. It was all about him. He'd gotten what he wanted, so nobody else mattered. In the worst case of those three, the owner of the school provided a significant amount (read: about 20 hours) of free instruction to the customer in order to patch up the relationship, thanks to our former instructor.
Before I started working for my boss, I was a freelance instructor charging $45/hour. When he approached me with a job offer, he said he'd start me at $18/hour, but I could expect more if I did a good job. I told him that was a big pay cut. He asked me what it would be worth to have an office, phone line, web site, nice aircraft, online scheduling, marketing, and insurance provided. I saw his point. I took the job.
I beat the bushes for clients right and left. I hung around the office, designed marketing material, followed up with prospective students, and generally worked hard. Before I had a chance to ask for a raise the owner bumped my pay to $20/hour.
I kept working hard. A couple months later my pay went to $22/hour.
I kept working hard. The owner asked me to become a manager. Now I make about $30k/year, set my own schedule, have every weekend off, and love my job.
From my limited experience, good help is hard to find. It's difficult to find an instructor with the perfect blend of technical skills, social skills, business skills, and work ethic. Every instructor *thinks* they have it, but I'd say less than 10% of instructors *really* have it.
When it comes to flight school ownership/management, there are plenty of sleezy places like you described, but there are also plenty of really awesome places. The problem is that the really awesome places don't get recognized very often because it's so much easier for a person to complain than to praise.
As with any business relationship, if both sides recognize the value of the other and are willing to compromise, things usually work out great. It's when one side gets selfish, narrow-minded, or unwilling to compromise that things turn for the worse.