I think a BPS is a very good gun - I have a few of them / and I really like them for young shooters that are left handed. They eject out of the bottom and they are usually cast neutral - so for a leftie, they fit pretty well.
However, I think that particular gun is a bad buy. The BPS lists new for about $575 and I see quite a few for sale new around $475 / but they are going to come, in the hunter model, with a 28" barrel and 3 Invector Plus chokes - meaning you can really do whatever you want with the gun - hunting, sporting clays, skeet, trap etc / and use it as a "defensive weapon". At $ 475 I think the BPS is a great buy.
There is a big difference for someone that wants a "defensive shotgun" vs a "fighting shotgun" - I'm not really into Fighting Shotguns / and would tell you that a BPS with a 28" barrel is ok as a "Defensive Shotgun" / and you end up with a versatile gun. For "Defense" you can take the plug out / it will then hold 4 2 3/4" shells in the mag for "OO" or slugs or whatever you think you need in the gun.
If you buy that consignment gun, even at $ 275 it will cost you about $250 for a new 28" barrel for it - and then you would have a short barrel for "Defense" or to set it up as a "Fighting Shotgun" - and a versatile gun but if you can't get his price down to $ 275, I say its a bad buy.