In March, I had a run of Duck Stamp plate blocks on
ebay with no takers at 20% over face. I then broke them up and sold two sets of singles, and have two sets remaining, which I will list in mid-September.
There's plenty of post-1980 duck stamps out there. If you buy, go for XF centering, and never buy them hinged, they would be darn near impossible to resell down the line. Ignore duck stamp first day covers, and duck stamps of other countries.
In truth, they aren't even postage stamps; they're revenues.