You should be fine in this case. I would find out the reason why he want's to sell it. If it's a money thing I would be more confident in the purchase and could probably get a better deal. Also, the 250 in .45 hasn't been out that long so that betters your odds. On top of that, it's a Sig.
When I buy a used gun, the first thing I look at (after I make sure it's not loaded) is to see how clean it is. I ask them if I can do a field strip and if it is clean in the hard to reach areas that is a + in my book. Look for any cracks, feel if the trigger is "gritty" and try to manually cycle some snap caps by racking it. Make sure there is not alot of slop with the slide and look for any unusual wear. Since you have new guns you know about how much you have shot them and the wear that it has cuased. When you look at a used gun that should help determine how much it has been shot. If they say they shot 500 rounds but it looks like they shot 2500, that tells me they are either lieing, didn't clean it properly or it was not lubricated properly.
Just buy it already.
