As a hiring manager, if I hired and fired people very quickly and in succession, and changed the job ad each time, I'd sit myself down and have a talk with myself that went something like this:
- "Do you have any idea what you're looking for?"
- "Do you pride yourself in treating employees like throwaway parts?"
If I answer "No" to the first point, and I don't ask for help from colleagues or peers, then I wouldn't want to work for me.
If I answer "Why, of course!" to the second point, I really don't want to work for me.
As a prospective candidate who knows only one side of a story (that a hiring manager appears not to know what he or she is looking for, and also doesn't appear to give people a chance), if the job is appealing to you on paper then you can figure out the mettle of the hiring manager when you make it to the interview portion and ask some questions:
- "You seem to have posted this ad a few times with some slight changes each time. How has your thinking about this position evolved over time?" -- If the answer is "I had terrible people try to fill the position" then you might wonder if this person is someone who should try to fill positions and manage people. If the answer is something like "the needs of the company shifted a bit, and the type of candidates I was seeing did as well, so I've been trying to match up" then you know the manager is trying something, and might give him or her the benefit of the doubt.
- "What are your expectations for someone in this position in the next 30/60/90 days?" -- If they're completely insane, by your estimation, then that's one data point. If they're reasonable, then that's another.
I think you see where I'm going -- on the surface, given what you have said in the question, this might appear as a situation to avoid entirely. But with a few well-placed questions in the interview stage, you can begin to see if what you see on the surface is in fact a bit distorted. And then you can make your own decision, as you progress through the process -- maybe even before the hiring manger makes one!