It is the same as buying a car with a broken odometer that your life may literally depend on someday...
I kind of thought this is what you're looking for.
My standard for any gun that my life might depend on is simple. It must fire at least 500 rounds without any kind of malfunction using the load I'll be carrying. It must do this from beginning to end with no additional cleaning or lubrication.
How did I arrive at that number? Well, it's not completely a WAG. Statistically speaking, you must have a population of 30 or more to have a reasonable sample. With an auto-loading pistol, you must remember that the magazine is part of the equation. So, because I use mostly a 1911 with 8 round mags, 30 repetitions of inserting the mag and shooting until empty would be 240 rounds. If you plan on carrying an extra mag, and you should, that's 240x2 which is 480 rounds fired. I just round up to 500.
Now, if you were to alter that paradigm to include a 10 round mag, it would be 600 rounds to ensure two mags of 30 cycles each. However, you can alter that by shooting full mags three times each (this gets you to 30 of just firing the rounds) and then down loading them to save ammo cost, but still get the benefit of changing the mags a bunch.
In the end it's an arbitrary number dreamed up by some lunatic (me) on the internet. Even so, I'd do this process with any gun that is new to me before I'd carry it. The actual round count on the gun is irrelevant.