So I am the most powerful mage on the planet. A merchant offers me an artifact that is too expensive for me to buy.
With some exceptions, what makes me, the most powerful mage on the planet, not just kill the merchant and steal his goods?
Important exceptions:
- Morality is out of the question - I don't mind killing people. But I don't want to kill this particular merchant.
- My relationship with the merchant does not matter (brother, father, sister, loved one, stranger, or a friend)
- Merchant should not be under a curse that will kill me or inflict any harm to me when I kill him
- Artifact cannot be cursed
- Merchant can be a normal civilian
- Merchant can be a powerful mage (but I'm the strongest mage, so power doesn't really matter)
- I am not afraid of crimes and punishment
- Artifact can be a normal item or a magical item
- I don't want to rob him either
So with these exceptions, what reason could make me rule-out the idea of just killing the merchant to steal his/her items?
Can you guys also help me add appropriate tags for this question? Seems hard to find a fitting tag. Thank you.

planet. He can't cast interdimensional magic, etc. He knows all kinds of magic but certain magic requires these artifacts. I'm asking for a good reason not to kill the merchant simply because my character's personality does not want to. If my mage can bend reality, create things on his will, then I should not have asked this question at all. – Bwrites Sep 13 '17 at 14:38