PlaneShift

General: As a computer scientist, I am so used to "3-slot exchanges", I was even surprised about people frequently using "2-slot exchanges"; of course it is convenient in cases of already full stacks or incompatible items, but trying it for items of the same type is already "risky" per-se, an averaging stacking expectable.

1.: Stacking same-quality items makes sense, to avoid wasting inventory slots; dividing items into classes of "whether or not stack different qualities to an average" may require a remarkable effort, I would doubt its implementation.

2.: Agreed.

3.: Not only enabling, but also specifying a quality difference threshold.

Setting status "New".

There is actually one more "follow-up" caveat connected with stacking items of different quality. When you are doing lets say juices with herbal, the NPCs will buy it for you for a price that is determined by resulting item quality. The higher the quality of the item the more the NPC pays per quality point. To get a maximum money from the juices you should avoid stacking them a and sell them one by one (check example below to see what I mean). I tried to do this, but it means a lot of place in the inventory (not that big problem) and extensive clicking on selling button to sell them one by one - it's rather time consuming. Perhaps if there would be a button "sell all" (not the whole stack, but all the items I see in my NPC sell list - with confirmation) it would help making this more effective. On the other hand I don't think that automatic quality averaging with alchemy and herbal products is a big problem, but just adding my experience here for the sake of completness.

The example:
You have three wragberry juices with qualities 137, 183 and 200. You can sell the 137 one for 162 tria (1,18 tria per quality point), 183 one for 234 tria (1,28 tria per quality point) and 200 one for 270 tria (1,35 tria per quality point). The sum is 666 tria. If you stack these three together, the quality of the stack will be averaged to ~173 and you sell one from the stack for ~214 tria that totals 642 tria.

Well stacking (and thus averaging) items is a definite must for crafters. Inventory space is much too limited (I'm not saying that's a bad thing and needs changing) for working with sensible amounts of material if you cannot stack the items produced. (You also have to think of raw materials that also are a product of some other crafting process in most cases) And while it may seem acceptable to exchange and store products and raw materials frequently in a smithy where you usually have storage in immediate vicinity it is surely not acceptable for crafts such as Alchemy, where you have to work with a large number of ingredients through a long series of crafting steps in a place remote from all storage keepers. And in my opinion averaging is the only approach when stacking items of different quality. I don't see a sensible alternative there.

Plus there is nothing automatic about the stacking as it currently is. You have one button with and another without stacking when handling containers. As for item exchange in inventory, it is indeed an expectable behaviour that you are stacking items of the same type when putting (clicking) one upon the other. I agree that you can indeed make a rash mistake there once in a while, but I also have trouble understanding the big surprise here. Any other behaviour I would consider unintuitive! As for the two-slot exchange, that is still possible and safe if you do it the other way around and take the unequipped item for a start and exchange it clicking the equipped one in the actual equipment slots. There IS already a technical hurdle implemented there that will keep the item from stacking with any partial stack left "below" the item you're working with that way.

When it comes to the desired protection/confirmation… While this surely makes sense to protect newbies from learning a similarly hard lesson, it cannot be made an obligatory standard, because it would hamper crafting routine a lot. If such a confirmation is introduced it MUST be optional and easy to deactivate.

In general I think trying to prevent all potential mistakes by technical measures will NOT result in the best gaming experience, however well-meaning the efforts. This strategy of simplifying things has backfired before, as the problems illustrate that continually arise out of the defaulting to "basic chat mode" when dealing with newbies. Just to mention one example.

With regard to the pricing matter … averaging naturally results in a certain margin of variation if you are dealing with rounded floating point numbers. Of course one can discuss whether 6 Tria (3%) difference per item as in your example is still acceptable. I think it is. And I happily pay that price for having the ability to stack and sell stacks in one click instead of doing it item per item, one after the other.