Sorry for posting this in Beta Status, but it's a good way to get it read by people. I wanted to say some words about the new vendors and to spoil a few of the secret recipes ;)
In this post, I refer to the vendors that you buy items from as "buy-vendors". The vendors you sell items to are "sell-vendors".
There are two types of recipes at the sell-vendors. If you hand in identified items, you get a number of currency shards in return. Types of mods have specific prices in terms of numbers of shards. Identified items can be worth less than their unidentified versions! This system is designed to not force people to drag every item back to town to sell. It is a great way to accumulate a few orbs (or scrolls) of wealth if you're running low, though.
With this first category of recipe, players are encouraged to learn what mods are worth what prices and to optimise their behaviour around selling those ones. For example, some mods are worth Alchemy Shards. You can sometimes buy items with those mods from the buy-vendors for only a scroll or two. It's entirely possible for a clever player to be rewarded with a guaranteed alchemy orb or two if they keep an eye on the shops as they level up.
You get a Scroll of Wisdom for each five white items that you hand in (via Scroll Fragments that can be kept in partial stacks). Three Scrolls of Wisdom can be traded at the buy-vendor for a Portal Scroll. If you find yourself running low on scrolls, remember these recipes.
The second type of sell-vendor recipe is far more complex, but can be really lucrative! There are currently 33 different recipes in this category, and they're designed to reward players for experimenting, planning what items they pick up and completing sets of items. We want to keep most of these recipes secret, but are willing to give some examples here to give an idea of what would work.
Handing in items of a certain class (armour, weapon, flask or gem) whose combined quality is 40% or more will yield a quality upgrade currency item of that type (for example, a Blacksmith's Whetstone). I was playtesting with this recipe last night and found it to be really rewarding to get these decent currency items in return for keeping an eye out for high-quality items that I would otherwise ignore.
Another recipe is that you can get an Orb of Augmentation by handing in a rare, magic and normal item of the same base type. This means that whenever you find a rare item, you should look for magic and normal versions of that base type so that you can get better value than the default hand-in price for a rare item. There are other variations of this recipe that give better rewards.
When trying to think of what recipes might exist, consider things that sets, runs and other patterns. The two examples above rely on "quality" and "rarity" as different things we're testing. There are a lot of others. There is a recipe to generate almost every orb (including very high orbs).
I encourage you to share any recipes you find with the rest of the community (or profit from them privately?) Someone should make a thread with all known recipes that can be kept updated.
Also, bear in mind that we've only added the first 33 of potentially hundreds of recipes! There will be plenty of new ones added (I intend to add one that allows downgrading of low currency items to scrolls pretty soon). We will also adjust ratios and prices based on feedback.
Edit: By the way, if you don't have room for the received items after the traded ones are removed, the extra ones get thrown on the floor... We'll fix this later! This doesn't happen often in practise.