Slightly off topic, but here's a list of some items which sell which is good to note:
https://forums.d2jsp.org/topic.php?t=104981333&f=272In short every single level 35+ item will sell.
There's a reasonably good chance most level 20/25/30 items will also sell.
The reason for this is transmuting, where with enough proficiency, you can turn an item into essence which is then used to reroll items. I'd recommend avoiding this for the time being and solo'ing and selling the items found, but if you're willing to dump 500+ hours into transmuting it can become very profitable.
The "white"/wellable items are those without stats for example:
Tempered diamond dagger
Level Req: 45
Damage: 159 to 279
So it has no prefix of magical and it has no additional stats, the reason this is valuable is that it can be thrown into a well to initiate a "boss fight" which will then drop the item thrown in and potentially give you side drops.
We call the "pools of water" wells, you drag an item onto it to initiate the fight, you can also fish in it, but there's no point unless you have high fishing proficiency and should use the town fishing until then if you want to skill fishing.