Diablo 2X has a barter economic system, which means there are no set values for any items. The closest point at which D2 ever had a real "currency" was back in the pre-Expansion v1.06-1.07 days when everyone wanted and traded with Stones of Jordan. However, that wasn't because the SOJ was real currency but because the SOJ was always in high demand. The SOJ dropped from effective "currency" status (as did duel leech lances and Iceblink) with the release of the Expansion, since other items were of equal value and competed with the SOJ in demand.
A barter system creates problems for us because, in real life, we live in a currency systems. In a barter system, the values of things traded depends entirely on how much someone wants them and not in their absolute value in a universal and stable currency. In short, the value of an item is based on its use value for each individual character. Now, some items are nearly always useful, such as Harlequin's Crest (Spelling?) and so are always valuable. On the other hand, trading an Arm of Leoric to a Barbarian is trickier. If the player using the Barb doesn't like playing as a Necro (perish the though), then he likely will not trade anything valuable for it. Now, let's say the other player, the one offering Leo, is a necro. He likely expects something valuable for the wand because it is useful for Necros.
Where does that leave our traders? Well, it's never this simple. The Barb may know someone who wants the wand but may want to take advantage of the Necro by offering something to the Necro the Necro views as less valuable than the Leo he is offering. Let's say the Barb is offering a Thul rune for the Arm of Leoric. Most would say that the Thul rune is hopelessly less valuable than the Arm of Leoric. However, let us suppose that, after doing 100 Countess runs, you've gotten all the high-end runes to Heart of the Oak, but the Thul eludes you. Frustrated beyond belief and unwilling to do yet another countess run, the necro gives in to the Barb, and makes the trade. The Barb later trades the Leo for Storm Shield later on. Did the necro get screwed?
Well, no. Remember, the Thul, for you at that moment, was worth the Leo. And, for that matter, the Leo, which has absolutely no use for the Barb himself, proved useful to the Barb in its ability to get him a nifty shield. Furthermore, when you traded the Leo for the Thul, you actually didn't just get the Thul--you got the Heart of the Oak Runeword. Now, when you look at it that way, trading the Leo for the Heart of the Oak is a decent trade.
What we learn is that the value of a item is based on its relative use, or the value of the item at that moment for the player. That is why you usually don't find helpful guides on the value of items. The one on the trade forum only includes those items like Shako that are always useful. The currencies now used are small charms that are useful, the 3/20/20 variety having replaced the 290 psn dmg after the 1.10 patch. Perhaps gold was supposed to be a currency when D2 was originally released, but that is obviously not nor was it really ever the case. The stores in D2 only in very particular instances provided opportunities for getting good items, but gold is easy to get, unlike Shakos, making gold really something for buying tps, repairing weapons, and raising deceased mercenaries. All of those can be done by selling two or three magical orbs with inherent bonuses.
A final example from my own experience: I traded a +1 to Summoning Skills charm the other day for Sigon's Helm. Most people would view me as being completely ripped off. The truth is that I have a lot of these, and my summoner has so many charms that he can't pick up a 2x4 item when he's in public games often because I have accidentally picked up a Fulminating Potion that blocks my available inventory space (causing me to swear very loudly). This happened to me so many times, I just decided to trade out a charm for an item that I inexplicably could not find, Sigon's helm (some people complain about finding nothing but Isenharts and Sigons on this channel--who are these people? I keep finding Irathras and Infernals, but just the completely useless ones). That completed the Sigons set on my struggling low lvl wind Druid. Now, I can play him again (I NEED TORNADO! I HATE LEVEL 22!), and this guy has a charm he really wanted. If he goes off and trades that for something like ViperMagi or something, then he got a good deal... but his good deal doesn't detract from the particular use value I am currently getting out of my newly completed Sigon's set.
Remember the value of an item is based on a PARTICULAR character's needs and NOT the needs of others. Until Blizzard introduces DiabloBucks, we have to live with our barter economy, SOJs and Isenharts, Io runes and Thul runes alike.
