the meeting in the valley

Genesis 14 

17After Abram returned from defeating Kedorlaomer and the kings allied with him, the king of Sodom came out to meet him in the Valley of Shaveh (that is, the King’s Valley).

 ¹⁸ Then Melchizedek king of Salem brought out bread and wine. He was priest of God Most High, ¹⁹ and he blessed Abram, saying,

   “Blessed be Abram by God Most High, 

   Creator of heaven and earth.
²⁰ And praise be to God Most High,
   who delivered your enemies into your hand.”

   Then Abram gave him a tenth of everything.

 ²¹ The king of Sodom said to Abram, “Give me the people and keep the goods for yourself.”

 ²² But Abram said to the king of Sodom, “With raised hand I have sworn an oath to the LORD, God Most High, Creator of heaven and earth, ²³ that I will accept nothing belonging to you, not even a thread or the strap of a sandal, so that you will never be able to say, ‘I made Abram rich.’ ²⁴ I will accept nothing but what my men have eaten and the share that belongs to the men who went with me—to Aner, Eshkol and Mamre. Let them have their share.” 

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On his return, Abram is met by the (rather surly) King of Sodom and also Melchizedek, King of Salem (Jerusalem, perhaps?).  Melchizedek is given the title of priest, the first direct mention we've had of such a role.  He brings not bread and water but bread and wine to honour Abram.  He blesses him by God Most High -
El-Elyon. (El was the 'top' Canaanite god but also a way that Yahweh is referred to in the Old Testament.)

Abram's actions are already being accompanied by blessing.

Abram gives Melchizedek a tenth of everything as a response; does this feel like a tithe?  Another trackback?

Abram rejects the offer of the King of Sodom and swears by Yahweh, El-Elyon (more specific) that he would not accept anything from this king's hand.  The King of Sodom will never be the source of any prosperity for Abram.  He will only accept the food that the men have eaten, and asks that his allies (apparently present with him in the attack) should have their share.

Does Abram's rejection of the King of Sodom's offer signify that he disapproves of Sodom and is aware of its reputation?  Or does he not want to receive anything from an enemy, instead relying on blessing from God (which is what Melchizedek offers)?