Personal experience (anecdotal evidence is another way of putting it) varies. None of the Vets I've been acquainted with had any problem with the M9. All said that some were in better shape than others, but all worked as advertised. I will say that one and all were Marines...noted for keeping their weapons in good shape.
When my #2 son went into the Marines, (had an MP DOS), I bought him a M92FS Beretta to keep for practice. That gun now has had over 7000 rounds through it, by actual count, and still functions just fine. It will still hold 2" gps at 25 yds from a rest. We've neither repaired nor replaced anything on the gun.
YMMV, but that personally owned M92FS and those that he used in while on active duty with the Corps were first rate side arms...albeit in a marginal caliber...(that's the old warrior in me opinionizing).
Rod