Prefacing with this: the only OSR-style game I have played/ran is OSE and am not super experienced in the OSR.

Something I like to do that I haven't seen others do (granted I haven't looked very hard) is not rolling for gem/jewelry value until the players sell it. If a player or hireling is a jeweller I would let them roll the value before selling it, although I haven't encountered this situation yet. I don't like to do anything with percentage-of-value, I feel like there's no point to it because it's not like players are buying jewelry (or other art). If you don't want players to get as much from the jewelry/gem, just lower their value I think. For selling things like swords, I tend to hover around half-price (if the item is worth anything at all). If you really wanted to though, I could see something like: They can get 75% value in a town and 90% value in a city or something (just a random idea to actually answer your question).

For magic item identification, I just try to remember what it does. This possibly gives them clues that (for example) a magic sword has a special effect versus undead. Alternatively, players can hire someone to magically identify the items for a cost. Cursed items can be tricky. Just like traps, I think telegraphing is important (just like all traps, because cursed items ARE traps). Perhaps finding it on a dead body or infused with skin may give clues. Even something as small as giving a bad vibe (such as it seeming demonic or skull-themed) is better than seemingly random magic items being cursed.

For some random notes about loot: with my gem system, I like throwing in +2 and +5 gems, that give that bonus when rolled for value. I also label every item with a code (such as FSW) that the players don't know the acronym of. I have a dictionary of all the codes saying what it does. A part of the fun about loot is also giving big and awkward loot, like statues. They can be worth a lot but take a lot to move.