Free trader is stocking Goya, Chagall and Cezanne at last (3,6)

I believe the answer is:

art dealer

'free trader' is the definition.
'art dealer' can be an answer for 'trader' (art dealer is a kind of trader). I am unsure of the 'free' bit.

I cannot understand how the rest of the clue works.

(Another definition for art dealer that I've seen is " one who has a gallery, maybe".)

I've seen this clue in The Guardian.

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