Whenever I see free shipping, I know I'm going to get charged for each individual piece I buy to be shipped but it will all be sent in one box. Free shipping is a poor tax. That said I have some tools I sell, a pack of 5 for $5, Shipping in the US is $5-6, but it would be the same if they bought 20 of them. If I do free shipping I'm going to change the price to $12 in the US and $35 in Canada That box of 20 just got MUCH more profitable. This is what other people do.
I am very aware of this when shopping for myself, and I don't want our customers to feel like I'm taking advantage of them.