Stainless or aluminum keg?

[chris_zx2]

Guys I know there are a lot if topics about this on here and I have read most if not all of them.
I have access to kegs but need to make sure they are stainless. Unfortunately they are not mine so I cannot perform the scratch test or the muriatic acid test.
On my next visit I will try the rare earth magnet test which rad mentioned in one topic.

What I really want to know is if there is a way to tell based on the beer that was in them? I'm in Canada and the only american beer they had was Sam Adams. They do have Guinness which I have seen people use on here. The real question, I guess is, does it matter where the keg is delivered or will all Guinness, for example, kegs be stainless?

Thanks guys. Oh and moose if your still looking let me know and we can maybe price out shipping