Is there a verb for vendors shouting aloud in a market?
Like "one pound,one pound only".
And is there a noun for this kind of shouting? Peddling words?
Thank you in advance.

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I'd say barking or shouting.  Hawking is a very appropriate word but does not require that the person is shouting or being loud.

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I think the phrase you're looking for is "hawking their wares."
See the fifth set of definitions: http://www.merriam-webster.com/dictionary/hawk

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We Aussies have a lovely word for it: "to spruik".

A person who spruiks is a spruiker.

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Look at this article on the "Arab'' vendors of Baltimore.  There are some great links in the article.
http://en.wikipedia.org/wiki/Arabber

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