RE SteamTrades Rep Voting - Clarify whose responsibility it is to determine region locks

I was under the impression that the person who is trading the game away is the one privy to the info on if it is region locked or not, and thus it's their responsibility to divulge that information?

If he trades the game as ROW, he should deliver a ROW key, doesn't matter what he knows or doesn't know.

For me it is the responsibility of the one who trades the game away.
In the rare cases I had region locked games, I always made sure to clearly state that those keys were restricted to a specific country or region.

I agree the person trading away is responsible but isn't saying "I am in Asia and will not be held responsible for any locks outside of Asia." equivalent to saying asia locked? Anyone not in asia that doesn't check before hand to make sure there aren't any locks for the game in question is at fault in this case.

Then again, in Roman law: ignorantia facti excusat, that is if they traded the key as ROW convinced that it is ROW, then they should be excused. In fact, any agreement made under a mistaken understanding of the facts is voidable. So yes, they should be excused BUT also they should return the key they traded for, as the agreement is void. Won't be that easy if they already redeemed it...

It's a pain in the ass. If you request a gift link from humble bundle it warns you who can't activate it. If you request a key it doesn't give you any warning. But even the warnings from gift links aren't reliable as they sometimes don't match the actual restrictions on the key because apparently some publishers can't be bothered to give Humble Bundle the right information. And other official sellers might be quite good at giving the right information (Bundle Stars) or not give a shit (GMG).

Due to the complexity of these issues traders should be open, honest, understanding and mature with each other about the problems that may arise. But that isn't actually going to happen any time soon...

The person who is the seller IMO.
Caveat Emptor is often cited but that is a bad excuse.
Using that benefits shady practices and disregards the efforts by people who try to be fair and honest in their discriptions and who want a level playing field for seller and buyer alike.
Edit: The example above: The vendor is just too lazy to check the product they are offering and is trying to shirk off their responsibility with a global disclaimer. As little effort done as possible.

In some cases, the one who owned the game thought it was the responsibility of the person who was receiving the game to know whether the game would be region locked. One of them trading it away had a disclaimer on their trade page saying "I am in Asia and will not be held responsible for any locks outside of Asia."

Now, personally, I wouldn't ever trade with that person, mainly because that's a pretty crappy disclaimer, and because I'm not in Asia. However, someone did, got a region locked game, and didn't feel the blanket disclaimer really holds weight since the trader didn't say that the game itself was region locked. Personally, I agree -- I believe it's up to the trader to say if a game is region locked. A blanket statement doesn't really make sense.

This.. is actually a really simple scenario to sort out, at its basic principle.
The person trading the potentially region-locked game has the obligation to clarify that the game is or may be region-locked, and that tradees should be aware of that fact. If the trader doesn't offer that disclaimer, then they accept full obligation for the region locking and of offering equivalent replacement. After all, they offered a product and were unable to deliver the product that was indicated.
If they do offer that disclaimer, then responsibility lies with the tradee, who failed to properly consider the circumstances of the purchase.

It's the exact same legalities and considerations that go into purchases and trades through any other medium. There's really nothing special about approaching the matter on Steamtrades- obligation for details is on the person offering, obligation for reading details is on the person taking.
It's why I can get (and have gotten) a refund on a purchase which mislabeled console compatibility, or a refund on a purchase which mislabeled quantity of products in a batch purchase, or so forth- if terms weren't met, then fault is on the seller. If I simply misread or "brain-farted" or so forth, fault is on me.

If it's in the middle ground, where the disclaimer wasn't entirely clear, just decide if there was enough detailed offered that the tradee should have known to ask for more details. If so, then favor the trader. If not, favor the tradee.

Now, putting aside general practices for a moment, the fact is that anyone participating in a trading-based interaction who has concern that their product may be region-locked should most certainly offer their product first. For this particular scenario, you've got someone offering too-ambigious phrasing, refusing to go first, and apparently refusing compensation. Regardless of whether scam was initially intended, the trader clearly ended up scamming the tradee by the end of the matter (based on the interpretation I got off the data you provided). A negative reputation mark against the trader should definitely stand until it's clarified that some attempt at compensation or refund was made.
After all, when considering what reputation marks we upvote and downvote, we have to consider "If this mark is removed, would it potentially hide a pattern of inappropriate behaviors"? Our obligation on reputation marks is foremost to sustain any reasonable concerns with functional premises. As far as functional premises go, "the trader had a shitty demeanor during the trade" is reason enough to sustain a negative review. The only requirement for a reputation mark is that it relates directly to a trade; so long as the tradee has functional and clearly explained grounds for discontent, the downvote should, as a general rule, stand. [In this case, with a poorly explained disclaimer, not ensuring the situation was handled well in the trade itself by offering clarification or to trade first, and an unwillingness to sort out the matter offers quite a fair number of functional grounds for discontent, even if the trader was sunshiny and pleasant all the way through.]