So, there are a few underlying economic principles to consider regarding trade. Then, there is the “experience”. I’m not sure what games you played that you had such a wonderful experience trading items, but most of the ARPGs and MMORPGs I have played left a bad taste in my mouth metaphorically speaking.
Let’s start with Econ 101. Supply and demand. If you have too much supply then demand is negatively impacted. This mostly negates the purpose of trading since you can just find things yourself 99% of the time. In order to rectify that, supply is artificially diminished to encourage trade. What subsequently happens almost every time, is that there ends up being a small handful of people and bots that control the marketplace. You can curtail this with annoying restrictions, but even if you made it perfectly balanced it is still inherently skewed towards those who get lucky drops. POE is a great example of this. I played with a friend a couple years back and we both went through the season at the same time. I had more playtime, but my friend got an item that shot his progression ahead by MONTHS, literal months. It was like winning the lottery. He didn’t earn it, it just happened. Yet I got jack squat. Why was I being penalized even though I had played more and advanced further?
Now, to be fair, I get RNG and how it relates to drops and I am okay with certain levels of inequality between players. What I am not okay with is a lottery system to gear my characters. If I want an item, I should be able to obtain it with a certain range of time and effort. The only time trade benefits me is if I end up being an odd outlier to the expected outcome of a specific item and can mitigate that through commerce. The problem is that outliers are a niche that cannot be served by large, active trading community since it it diametrically opposed to a formula of itemization whereby the vast majority of players can reasonably obtain what they want. Therefore, I submit that the solution to this is not to fiddle with trading, but to create a system in-game that facilitates the targeted acquisition of specific items.
On the topic of getting specific items, Marvel Heroes (a once phenomenal ARPG) had 0 trading. Each person got their own items and that was that. Instanced loot was great and progression happened by doing activities such as weekly events, raids, and other endgame content to acquire a specific resource. This resource could be traded for blueprints that allowed the player to spend credits to upgrade their items to a higher ilvl. You could also exchange uniques for a random unique. There were later ways to influence the outcome, such as trading 4 weapons for a weapon or 4 boots for boots. And if you traded character-specific uniques that’s what you got, but if you trade ubiquitous uniques then that was what you got, or if you traded a mix then the outcome was random. As you got into harder content, you received so many that you could roll until you received what you wanted. This was not my favorite system, but it worked and trading in this fantastic ARPG was not a thing. The ROOT problem of supply and demand for itemization was addressed.
I have also played games where auction houses existed. Many many many MANY games have had those or some form of those. Player shops and peer-to-peer trading is also a thing, but the auction house is the pinnacle of trade. I think we all can recognize that the problems with that system is that it disincentivizes you to PLAY THE GAME, which is why we are all here (I should hope) in the first place. It is far more lucrative to play the auction house. Moving to lesser trading options, like the previously mentioned player shops and person-to-person trading, slows down the pace of monopolistic acquisition. It also becomes a pain in the rear to get something you want. You also have to worry about scams. D2 was a game I traded heavily in for a long time. The arbitrage opportunities of the undeveloped trading system presented a fun minigame of going channel to channel and hunting for bargains. I assume this shoppers high is what you ultimately seek in some fashion. The downside is that it was time-consuming and you had to be wary of people trying weird ways to jack your items or rip you off. There are measures you can implement and Warframe actually does a reasonably good job of limiting trade. It is the closest example of any multiplayer game I can think of that has stable-ish trade. Even then, it is far from perfect. It’s annoying to use, you have to have a 3rd party website, and you still have to check everything over and make sure you aren’t being tricked or ripped off. This raises the question - why do I even use it then? Well, that’s easy. The answer is because the time and effort to go farm some pain in the butt items I want can easily be negated with a few bucks in IRL currency. That is not what this game needs and the ONLY reason it’s such a pain to farm these items and so time-consuming is because it was artificially prolonged and obfuscated to encourage people to spend real money. That’s a terrible system, ESPECIALLY for a game you have to buy outright.
As for negative trading experiences, I could talk your ear off with the shenanigans I have gone through in a veritable cornucopia of online games. Off the top of my head, there are “drop” trades for important or restricted items, players swapping out items that look similar, having trades cancelled then restarted multiple times to trick you, doing enchantments that don’t stick but take your gold, being bombarded by fraudulent trade requests in neutral areas, playing the “I can’t trade this in the window for X reason so give me the money first”, or any number of other asinine attempts at thievery. I am not looking for another round of those problems or trolls that simply want to waste everybody’s time. Even auction houses are not immune to such things. In most online games there are things you have to be on guard for, like decimal point finagling or listing a bunch of the same item in one currency then having the last stack be in a massively different denomination of currency.
My point with all of this is that trading does not just “happen”, which you have already acknowledged. It requires changes that make the game WORSE for players in order to facilitate monetization or a valid, functional trading economy. I do not want that in my ARPGs. It either leads to lottery drops, AH simulator, or shady back-alley deals where you hope you don’t get e-mugged. Some people like the thrill of that stuff, but I would much rather just play the game and enjoy it for what it is. If you want to have a system whereby you can trade items you find with friends in a VERY limited fashion then I believe that could be an acceptable compromise. However, having large, open trading systems alters the game too much in too many negative ways to be worth it in my humble opinion.