It's a good thing that a digital checkbox on a site form isn't an actual mechanical device, or the checkbox on sites like FeeBay and Crapazon to filter by: FREE SHIPPING would be worn out in a week. Absorbing the shipping costs on orders over a hundred dollars is very effective for an online store. Easily recovered by the increase in total sales. Recovering shipping costs on smaller orders appears to be a tougher nut to crack, on the surface of things. Thousands of FeeBay vendors are doing it, though, with only a slight shift in the business model. They don't use FedEx and UPS just because they'll come pick it all up for them. They use cheap, but effective packaging and shipping methods and make tons of small sales, which keeps steady sales coming in all year long. It's often called "economy shipping" and if you can stuff that product in a bubblewrap mylar bag/envelope that a bald eagle can't get open, then the customer will get it in an acceptable time frame. You can always opt for the more expensive shipping methods if it's something you positively need in a certain time frame, or that you really can't afford to have damaged enroute.
The problem with some sites is that you are never given the free, economy shipping choice. Not even the non-free economy shipping choice. Smaller items end up costing as much to ship as the price of the item. Personally, I go elsewhere. I nearly always find a source for the product with either free, or very reasonable shipping. There is one site, where we all know the coupon codes, and everything ships free. Even that mini-carabiner we gotta have between paychecks. And it still comes in their usual packaging materials. I won't mention their name, but their initials are TreeStuff.com and it's going to be damn tough to lure me away from them, unless the concept of free shipping sinks into your business model, because I know how to use a calculator and add up what those shipping costs end up running me every year. You don't want to dip into the profit margin a little bit? Fine. Neither do I. My profit margin isn't even in the ballpark of yours, and never will be, because you're the one getting wholesale prices on the stuff I need, not me.
I do buy from other sources, and I don't always get free shipping. Usually it's because my favorite source just doesn't carry the item I need. But the bulk of my purchases will always be from... well, you know who.