Final Fantasy 15 – How to Make Prompto Stop Using Certain Filters in His Pictures

There are no "random" quests and the only repeatable quests are the hunts, if you count those as quests.

The rescue quests, where you find people in the wilderness and give them an item or the broken down car quests arent really random. They unlock at specific chapters and points in the story. There is no indication where they are and you have to "stumble" into them, but they are always there after you reach their unlock point. They unlock in stages, so you may go past an area several times and they wont be there, then after you reach a certain point in the story, the quest will suddenly be there. This isnt random, but locked content. Many of the sidequests actually work this way, you can just see those on the map, where these two types of quests you do not.

Hunts are the only thing that is really repeatable. They arent exactly "quests" imo, as they dont count towards the sidequest trophy count. As Kerwan mentions in their comment, you get reduced rewards for every repeated hunt after the first, but you can do them as many times as you like.

There are, in fact, certain treasures that are used in quests or to upgrade weapons (also considered quests).

I found a list of all of these "Don't sell" treasures in the game here:

• Barbed Scythe
• Cactuar Needle
• Coeurl Whiskers
• Cylinder
• Dynamo
• Earth Gemstone
• Glass Gemstone
• Magitek Core
• Magnetron
• Metal Scrap
• Monster Claw
• Repair Kit
• Rusted Bits
• Sky Gemstone
• Spiked Armor
• Sturdy Helixhorn

Thus, it looks like all other treasures are able to be sold without worry.