Haggler is an extremely useful late game skill. You save 10% at level 2 on anything you buy. I must have bought about 100k worth of items, if I didnt have haggler, I would have spent 50k on gear and another 50k on materials for elex potions and health and mana potions and another 10k on weapon upgrades. So I ended up saving 10k because of haggler. So if you have the attributes to get haggler, I recommend getting it, imo it is well worth it.
I'd say it depends on your style of play. I can see how it would be more useful for people who are trying to get through the game at a faster pace. If you're taking your time and exploring everywhere though, you'll never be short on money.