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Amazon does use more than 140 characters to present a product.

And often has reviews on the same page.

The reviews are the key. I always jump straight to the reviews. Half the time I never read the item description.

You can always add a link to the tweet for more details.

And then you can buy from the page with the details. Forcing you to go back to the twit to buy would be a bad idea.

Embedding the buy button wired up to your twitter account might not be so awful?