Thanks, that's the calculator that I used. At many weights/sizes, for US destinations the FedEx tab shows no rates.
I just signed up for Chit Chats. They don't allow shipping to domestic Canadian addresses, because I don't have a business, just selling some items on eBay but not a store. So, I'll explore it for U.S. and International destinations.
Do you ship only to U.S. and not to other International destinations? It would be hard to do a flat rate for an eBay listing, since International shipping rates seem to vary considerably by destinations.
When you said that Chit Chats rates vary a lot only on heavier packages, the variability is based on what? The destination state/address in the U.S.?