I used to manage (not GM) at an AMF center in the Houston, Texas area. It is true there has been a history of high GM turnover at some AMF centers. A lot of depends on the DM you have. Another reason is AMF has the tendency to hire GMs from outside the bowling industry. Not exactly sure why, but have seen it happen too many times. They sometimes don't ever understand the business enough to take advantage of what is available.
The main trouble area I saw was in payroll costs. Corporate has an anticipated payroll cost that has seem more and more unrealistic lately. Most AMF centers I have been to lately have been severly understaffed, especially since it has been for tournaments and you would expect decent support. I currently bowl in the same AMF I used to manage and it doesn't seem too bad. Aside from Hurricane Ike damage, it is in good shape but during league, there are extended periods of time with no one at the front desk.
Lastly, just because you might net $500,000+ for a couple of years, don't expect new equipment when you think you need it. AMF does renovations on a rotational basis (or at least used to) and if it isn't your turn, you won't get a thing, even if your ball returns are crap or your scoring systems require people to sit at them during league play. Just part of the business.
If you have any specific questions, feel free to pm me.
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I am not a pro-bowler, but I do play one on BallReviews.com