What to look for in second-hand kegs?

Take as much of the keg apart as you possibly can. You can use wrenches to get the in and out valves off. You need to make sure the popets underneath the valves are springy and not all gunked up. There will also be an o-ring underneath the "out" valve around the dip tube. CHECK THIS O-RING. If it is all gunked up or degraded, then you will need to replace it, but that could be a big source of leaks for the keg.

Inspect the lid as the others have said.

This may seem obvious, but I've been told to ask for new rubber or just have the understanding that seals/o-rings will need to be replaced. It's normally not a big deal since they're so cheap relative to the cost of a keg.

I like to check that the in and out posts are indeed in and out posts. You can sometimes tell by the shape of the base-nut, but not always. It takes a trained eye to see the differences. You could always bring a spare bev and gas disconnect to help you.

Check the pressure via the relief valve in the center. I like to lightly press down with my finger nail on the poppets themselves to be sure they are springing and seat back in the hole correctly. (Not a deal breaker, as if they are a little dirty maybe they won't seal back up.

The last thing to look at is the welds. There is one long one down the side, and a couple around the circumference at the top and base. Just look to be sure they are silver like the rest of the keg and not rusty. Make sure there isn't a significant amount of grinding on the welds in places, as it indicated maybe a quick welding repair, and grinding out. The keg may still hold pressure, but it could be a cruddy job on the inside. Lastly look inside the kegs if possible to see if the welds look good too.

Thats what I do when picking up kegs. Or I negotiate for a cheaper price for an as is purchase where I don't "tear" down the guys kegs.

Look inside for welds as well. This can indicate if keg was ever punctured. I know this seems rare, but a friend of mine just ran into this.

Things I look for:

• Any sign the lid is bent or uneven. Also check the opening in which the lid sits.
• Are the posts bent? One keg I bought has a out post that lists off to one side, makes it kind of a pain to use.
• Does it hold pressure? My LHBS pressurizes the kegs out for sale, so I can just test the release valve to see if the pressure has held.
• Is it the same style as my other kegs? This is more of a personal thing. Different style kegs can require different o-rings, parts, etc. I try to avoid confusion by only getting kegs that are the same style.

If the place you're getting kegs from doesn't sell them pressurized, you could test the pressure by bringing a co2 tank and a bleeder valve.

If the keg is pressurized and doesn't seem to leak, that should be a good enough indication I think. Check that gas is released when the middle of the ports is depressed, and that the safety valve works, and you should be good to go.