Smaug tells Bilbo not to trust dwarves:
In return for the excellent meal [of the Company's ponies] I will give you one piece of advice for your good: don't have more to do with dwarves than you can help!
Smaug-The Hobbit: "Inside Information"
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Bilbo told Smaug a riddle to keep him distracted.
Smaug doesn't recognize the scent of Hobbit, although he knows what dwarves and men smell like.
A coat of mithril he was given out of Smaug's hoard.
In the cave he noticed it when he was invisible
Balin goes part of the way down the tunnel with Bilbo, and Bilbo takes one single golden goblet from Smaug’s immense hoards.