I feel like I'm missing something. On inexpensive items, there's a lot of listings where an item is being sold for $2-5 with free shipping, and the seller ships from within the US and has Top Rated Seller status. Like, look up "cable", choose buy it now, choose US only, and sort by lowest price.
If I ship a small item that I would somehow magically get for free, the lowest breakeven I can really find is $4.90. The least expensive domestic shipping method I can find with tracking is $3.59, and that's for a zone 1 (0-50 miles) USPS first class that weighs 1-4 oz. Go with an average of zone 5 which for 1-4 oz is $3.81, $0.54 final value if it's an 11% category, $0.30 transaction fee, $0.25 promoted listing fee at 5%, and that comes to $4.89. OK, top rated would save $0.05 on the fee, and maybe you get lucky and have a listing that sells without it being a promoted listing, so you could bring it down to $4.59. But, there's still a bunch of items listed cheaper than that by top rated sellers. Are they all selling those at a loss? Hoping people buy multiples so they come out ahead? Some get that, but many of these listings show almost everyone buys just 1. I get that some new sellers could be buying feedback, but I'm talking about sellers that are far beyond that.
Yes, I know about eBay's Standard Envelope, but that's only available for certain categories, and sellers are having nothing but trouble with it so far. Yes, I also know there's several other companies doing USPS Informed Visibility Mail Tracking like letter-track.com, but my understanding is these are the same as eBay's Standard Envelope, also with problems of the post office not doing acceptance scans so customers think it hasn't shipped yet and eBay strikes against you as a late shipment for Top Rated Seller status. Also, they are scanned last at the destination post office, but not at actual delivery.
