There's also this thing about the prices and S&H.
The prices differ for the same items probably listed by different sellers, say, one selling very low, and the other selling very high, and if you check out the S&H on the low seller and total it with the low price, it still computes the same as the one with the high price but with a low S&H or the one with the "Free shipping".
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All the same items even with different prices will always total at fairly the same price together with S&H or "free shipping"!