Suburbanpond.com offers specials on shipping in a variety of ways.
Flat shipping on the big stuff. In lots of cases you'll see $100 shipping on the big stuff. In most cases, it costs us a couple hundred to ship your item, but the flat rate shipping allows you to anticipate your cost of shipping on things like filters, and fish. What we "lose" in shipping, we can make up on the product. That is why we don't have flat rate shipping on little items with very little profit.
But when it comes to smaller stuff, shipping isn't that much between you and me, but it's the difference between profit and loss in most cases, so it's not going to be free.
Sure, the guys with "all free shipping" might get a little more business than we do this year. But next year they'll be packing up their offices because they spent their time but didn't cover expenses.
*If you're getting a special price on a large filtration item, for example, free shipping might not apply to a specially reduced price purchase. Additionally, if the item cannot ship by common carrier Ground rates, the shipping will also not be free