You can sell stone mined with a silk touch pickaxe. But you can’t sell smelted cobblestone to a villager with a stonecutter.
Linked issues
Comments
That issue is fixed with 1.13, stone blocks prior to 1.13 are bugged and that issue is being tracked here: MCPE-54617
That issue is fixed with 1.13, stone blocks prior to 1.13 are bugged and that issue is being tracked here: MCPE-54617