This league was the first one where I actually bothered with trading and Awakened PoE trade is really useful for it. It not only gives you a price suggestion in game (which is typically very wrong for rares), but it also lets you check current listings for similar items based off the your selection of mods the item has. The value estimate has a drop down that lists the what mod on the item might have value.
What I did was with pretty much every rare accessory(rings, amulets and belts) and jewels I would check to see what mods might be valuable, then check if any combinations are more valuable. Eventually you won’t need to check anymore and you can pretty much tell is something has good mods. I only bother trying to trade accessories that seem decent, which is usually +life or +ES and good resistances (either ~30+ of 3 types, or 40+ to 2 types) those can usually move for 1-5c easy. If you get good rolls you can get way more, but that’s either gonna be from a real good Rog or a failed craft that almost made it, that’s on a cheap base.
I only ever really pick up rare accessories and jewels, since they don’t take up much space and vendor for the same amount of alts anyway (and I always want more alts). Weapons and armor have access to different mods and so their valuing is a lot more tricky and nuanced, but 90% of gear drops are worthless and 9.9% might be worth 1-5c to the right person and that lasts .1% isn’t really worth trying for when you can’t really fit all the rares in a map in your inventory.
As such I’m not great at pricing weapons myself, but the value generally seems to be in: “+n to level of socketed x-type gems”, critical chance/multiplier, and damage conversion mods. There’s probably way more to it, but my build uses uniques weapons so I haven’t had a reason to try crafting weapons which is how I got a lot better a pricing accessories.
Armor is pretty easier than weapons. Look for good ehp numbers first (ie. +ES on ES gear, +life on everything else). Then resistances and defense stats (evasion and armor). Helmets can get “+n to level of socketed x-type gems” mods and “socketed gem are supported by level n x-support gem” those are good, but you’ll never get a good combo and other good stats from a drop. Boots can have movespeed mods and essential to their value most of the time. Body armor and Gloves are simpler, but can hit bigger values on defensive stats, so good stats for a ring are probably not great on body armor/gloves.
For anything not rare (div cards, currency, uniques, maps), it’s significantly easier as the estimated value is usually pretty accurate. My rule of thumb is if an item is estimated to be worth more than 10c, I’ll check the listings to see whether the lowest listings are old and to see what other players have recently priced the item at. I usually just vendor uniques worth less than 1c and throw the others up until I run out of space, but I have a bunch of tabs so I don’t mind sitting on them. If you don’t have space, vendoring 1c uniques is fine. It’s easier to sell alchs anyway.