How to earn gils om 50 level?

[Onyxys]

Spirit bond gear while running easy dungeons like CM, Prae, Wanderer's, and AK and sell the materia. Make two armor sets, one for spirit bonding and one for your regular gear. Switch to regular gear for bosses. Most people don't care what you're wearing for trash mobs. You can also farm tomes and buy the crafting items to sell. Potash and coke are popular right now.

Your only other option is to farm mobs that drop something worth selling or do battle leves. You will not earn gil as fast as gatherers and crafters, but these methods should pull in enough to keep you afloat. If these aren't good enough, then tough cookies.

There is no evidence that the gil sinks outweigh the gil fountains and that this will lead to an economic collapse. The economy is doing fine, learn to earn gil like the rest of us.

Non-convertable they are

[Zeille]

Non-convertable they are

I have no idea what you mean. BUY lvl 45+ white/green gear off the auction house that can be converted, equip it, run a dungeon and turn it into materia.