In your option , if you were me, which husqvarna 310 would you buy off intersurplus? I would want a 2 3/4in chamber 12ga. SxS. I have been looking at the ones on the site for a couple days and would appreciate your opinion. They seem to all be <500.
I don't want to recommend a specific gun to you but I'm happy to try to guide you in what to look for.
At the heart of any SxS are the barrels. This is because while everything else can be fixed (it just costs money) barrels that are not good cannot. The damage can be ameliorated (ie honing out pits) but can't be fixed. You will always have lost that metal. So the first thing I an trying to assess are the barrels. What gets said in the ad about the condition of the bores. A "mirror" finish on a $500 gun from before WWII is a double edged sword. Maybe they are mirror....that's a good thing. But likely the only way they get to be mirror is they have been honed out. And Canada has no proof laws protecting the buyer from barrels that are now too thin so as to be dangerous. One nice aspect of what I call Germanic guns (Germany/Austria/Sweden) is they tended to use high quality steel and they tended to make the barrels walls nice and sturdy. The downside is they may not handle quite as well as a more refined English gun.
Then I try to look closely at the wood to metal fit. One thing in particular I'm looking for is evidence of cracking in the wood. On older guns, the wood shrinks over time, lessening the size contact areas. That concentrates the force of recoil onto ever smaller bits of wood, increasing the likelihood of cracks. Look closely for cracks.
I look at the overall silhouette of the gun, checking the drop at heel, and I make sure I find out if not listed what the drop is. Given modern shooting styles, it should be about 2 1/2". More than 3" is a deal breaker for me. Lots of older guns, particularly American, have drops between 3 and 3 1/2".
If you are like me than the difference between paying $300 or $500 isn't a big deal if its the right gun. So after doing the above, I rank them by price and try to figure out why Intersurplus has priced one at $300 and one at $500. There is usually a reason. Then I pick one, knowing that if I receive it and I've missed something, I can return it for a full refund (except for freight). I have probably bought 8-10 guns from Intersurplus and it's predecessor Trade Ex. I have felt the need to return one.
Everything i have said can be applied to any gun you are looking at on line. Don't be afraid to call them up and ask more questions or for more pictures. Intersurplus and any good retailer should be happy to accommodate requests like that. And if you are dealing with a retailer who doesn't explicitly describe their return policy, ask what it is in an email so you get a written response. Don't just ask in a verbal conversation. you want written proof.
Edit to add: I find for myself that the longer I look at a gun on line, the pictures and the specs, the more I see. So I tend to go back for days on end, re-looking at listings that caught my eye initially. Sometimes on the 3rd or 4th look I see something that rules it out for me. Sometimes I see something that makes me buy it. Hard to put exactly into words but it's worth lingering over a few to see what they reveal.
Ive left out some of what I think are obvious things like does it lock up tight, are the barrels on face, do they ring when tapped etc. Common checks of condition for SxS shotguns. I have no idea how much you know or don't know. What I was trying to note were less common "must dos" that have really helped my buying over the years.