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Yes freshness does help. In your regards to your problem, best sellers are usually best selling items within your own business/site. So generally all these stats would be from your own business. Whats been selling and what hasn't been selling. If a certain product is converting on your site, it would make sense to show that it is a top seller to create more conversions. Lets say a visitor comes to your site basically to buy shirts, but one of your 'retailers'/brands sell more jeans than usual, then that top seller would not benefit your visitors. It is your business and you should use those implications to decide what to put on that list.