The solution is rather simple. Whenever you buy something off the market board yourself, skip the cheapest items. Buy from somewhere in the middle.

This behavior is something which is seen more and more often on a lot of crafting items on Odin. There can be a listing of items for e.g.

5497
5497
5498
5498
5500
5500
5999
5999
6000
6500
7000
7000
7500
7500
8000
10000
10000
11000
300000
300000

And whenever I'd throw up items in the range of around 7500, the items rapidly sell. More and more often you also see it back in the sales history of the item that it's not the undercut pieces which get sold. But rather more and more crafters become aware that undercutting is hurting their own business.

Unfortunately in the case of end products this effect is often still lacking. Consumables and such are more often still purchased at the cheapest pricing. The same goes for battle materia.