I noticed that crystals and mythstones have a selling price, so why can’t we sell it
Selling Crystals: well, for me, the only one I would even consider selling is Quartz, but I go through Diamonds so much that converting Quartz to Diamond is a better option (using them for Challenge Maps & Crafting). the only really big downside to selling Crystals is for when you need to do some Crafting and there are no Crystals, or you accidentally sell Crystals you didn’t want to and don’t have them when you need them.
Selling Myth Stones: Crafting Mythic Affixes is more important than getting Gold from selling Myth Stones. even using Myth Stones by themselves for their affix is better than selling them.
now, I just looked at the selling price of CS & MS, and wow, MS could sell for lots of Gold!!! but the thing is, in the early & mid game, you are converting the lower CS & MS to get the Rare & Ultra Rare ones, and in the late game, most players have a Farm Build that brings in more Gold than you could ever get selling CS & MS.
on the other hand, for players who have their own Ultimate Player Builds and don’t need to Craft Builds anymore, then selling CS & MS could be a good option for them. the best way for this to not be a problem, I think, would to put a switch in Options for selling/not selling CS & MS, so Crafters don’t sell them by accident and non Crafters can sell unwanted CS & MS.