Selling -

Some things are mere inconveniences, while others are one time only things....

- Where did you get the item if you remember? Can you get back to that place easily and get more? If yes... sell. The worst that can happen is it is in a recipie and you might have to come back and farm more later.

- Was the item dropped by a mark/quest/boss?... if so... maybe hold onto it for a while. It is unlikely you will ever get another, so maybe hold onto it for a while.

Arcana will be rare for a while, and later on if you buy something very expensive, it will start to drop like candy.

The issue with selling some things is the bazaar system.
If a item requires

2 swords
3 boomerangs
1 shield

and you are wanting to get many versions of this item.. say you need 3 of it. Well if you start selling the sword, and it is kind of rare, but lets say you get 4 swords and 1 shield, but only 2 boomerangs... you sell all of it. Well since you have not triggered the 3 boomerangs, those 4 swords all go in... and when you finally do trigger the bazaar item with the last boomerang it will eat up all 4 of those swords and count them as "2". They won't carry over to the second set of that item you want, all "counters" are reset to zero when you come out of the sell menu and a bazaar item triggers


Lets say you just sold:

99 swords
4 pieces of rock
3 stones
9 gems

and you sold that all at once, or just now got the pieces of rock and sold them.
Well a recipie might require
4 swords
3 pieces of rock
2 gems

Now your bazaar counter which used to look like this...
99 swords
3 stones
9 gems
0 pieces of rock

Looks like this after selling those pieces of rock
0 swords
0 gems
0 pieces of rock
3 stones

Now you have to farm 4 more swords, 3 pieces of rock, and 2 gems.. where if you saved your gems and swords and hadnt sold them.... you would only have to get 2-3 more pieces of rock.. i think 3.

- Final wording...
There are very few things that are one time only that I can remember in the game, and most are just inconveinances... meaning you will just have to go get more of a particular item.

In general its ok to sell storebought armors/shields/weapons.
You may want to hold onto armors with elemental properties.. such as halving an element damage on armors. And also those dropped from monsters, that you haven't found in stores.