I'm *guessing* it's a PSP turn-in police gun from Germany.
The PSP has a heel mounted mag release and no plastic heat shield on the trigger guard. I think the last batch of those guns were refinished in (silver colored) NP3, but you said this one was black. Some are stamped BYP - (Bayern Polizei if I remember correctly). BMI is another stamping - but that maybe just M8s. There are at least two different styles of heel mag releases out there and I think there may be one more.
IIRC, those were originally selling for less than $800, but that's a fine price for one now - at least in my area.
The P7M8 is slighlty different in that it has a heat shield on the trigger guard and an ambi mag release on the trigger guard. If it's an M8 for $800, snag it quick.
The P7M13 is the same as the M8 but has a big ol' butt and packs 13 rounds. If it's one of those for $800, avoid it like the plague and email me the name of the seller
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An M10 is an ungodly pistol in .40 S&W and I doubt seriously that's what this is.
In short, if you want a P7, I'd buy it. Some think the PSP is the best of the lot, but some hate it for the heel release.
Definitely head over to Park Cities Tactical for more info.
Check this thread:
http://www.parkcitiestactical.com/ubb/ultimatebb.php?ubb=get_topic;f=10;t=009862#000000
Check out the threads on the most commonly broken parts.
If I were going to buy it I would pop out the firing pin and make sure the bushing is OK.
Make sure the squeeze cocker works and dry fire it.
If you've never handled one before, you may be surprised how difficult it is to retract the slide. That's normal.
Good Luck