> It's a different strategy. Prime is an investment up front, so it puts people in the mindset of wanting to come up ahead. By buying full Prime, you've essenti

> It's a different strategy. Prime is an investment up front, so it puts people in the mindset of wanting to come up ahead. By buying full Prime, you've essentially prepaid $120 in shipping costs, so you want to take advantage of it and order more than $120 worth in free shipping. Some retailers do this too, mainly warehouse clubs (e.g. Costco and Sam's Club).