post offer retention...?!

It may not be the in thing in these times of recession Circa 2009... But we all know that it was common to have employees come back to the management with a decision to exit owing to a higher compensation.... and the management, through HR comes back to the employee with a more attractive compensation and other employee retention tools.... 

I have heard a few cases then and even now, where the line/function commits something to the employee, and once the employee concurs, and almost decides to stay back, HR ups the ante and says that it was not privy to the decision.... and the candidate is at a loss morally, and monetarily too....

Looking at this, guess candidates need to be clear if they will stay or leave come what may....   and not tread in ambiguity, screwing up their career and stature both with the present employer and the future employer too......