When a new seller starts selling on Amazon it means they are introducing new product in Amazon market, with new listing and this is where Amazon gives that new seller a benefit of doubt on the basis of the fact that may be this product has potential. Similarly, when the first inventory of that new seller is live amazon gives that new seller maximum exposure (Amazon rank them better on different keywords) and this period lasts for almost 30 to 45 days (depends on product category). Furthermore, if you run an auto campaign (depends on the seller) Amazon targets the product on different keyword and if you get maximum sales in these 30 days Amazon pushes you on different keywords, placements and ads and you can organically boost your ranking