I have Ginger pinking shears I bought as a set on ebay --- they are so stiff and hard to use. I wish I had my cheap Fiskars pinking shears.
I've been told they loosen up with use.
They have not.
Regardless -- they are guaranteed, Gingher will sharpen them if you send them to them. The address is on the box.
I don't know if there is a similar thing for your Wiss shears.