I have one myself. The key with these guns seems to be price. I paid less than two hundred for mine.
It's hard to tell wear on the '37's as they are all steel. Most cop guns were carried a lot and shot very little.
I would ignore surface wear and take a very close look at the stock. The area where the walnut touches steel is key. Make sure it's not oil soaked or soft. No splits, cracks or loosness. (buttstock) The foregrip is important, just ensure it's not cracked or loose.
I bought one for a left handed buddy that appeared brand new.
If you have a selection, don't be afraid to sort and pick.
There were a few that had full choke bores. Mine has that feature - just be aware that it is really full! You will find that the full choke models will not pattern OO buck very well - but do fine with # 4 or # 1 (my fav).
Look hard at price. If it's not more than two hundred, you may have a good deal. More than that and it gets kind of iffy. There are very few add-ons for the M37's, so what you get is what you've got.
Hope this helps,
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[This message has been edited by Gizmo99 (edited December 02, 1999).]