We had to replace one of our heat pumps earlier this summer. It was timed rather fortuitously, as I had recently replaced the filter with the last one we had on hand.
I generally buy the filters by the case, first comparing a local HVAC supply house against the going price on Amazon. There are several companies that sell filters on Amazon, but upon arrival I always get a case that is direct shipped from the manufacturer (Glasfloss), on behalf of the seller. This time, some company in Florida was the seller, but I got the box direct from the Glasfloss factory in Dallas.
Our new heat pump requires a 20x20x2 filter. A mistake was made somewhere in the ordering process - I am fairly certain that I ordered the correct size, but there is no size designation on the order confirmation or invoice - just a part number that they now claim equates to what they shipped me, which is 16x16x2 filters. A dozen of them, in a giant box.
Once they arrived, and the size disparity was discovered, I requested, and received, return authorization. I trotted down to the local shipping store only to be told that shipping a box that size was going to cost me considerably more than I paid for the merchandise. I took my box back to the car, returned to the office, and began to get quotes at my company's negotiated rates through Fed Ex and UPS. The best rate quote was $30, about half the value. Now I am stuck deciding whether to cut my losses and get a net refund of $30, or list them on Craigslist or something and have to deal with that hassle.
Which brings up the bigger issue, how much are these things marked up? I save about $35 per case over the Home Depot and Lowe's prices, by buying online. And, while I am sure that Glasfloss gets a heck of a good shipping rate, it can't be free. And, the Amazon re-seller has to be getting their cut somewhere in there. Are their margins razor-thin, or are brick-and-mortar end consumers getting completely screwed?