I prefer the Champion Flyer over the straight B17, YMMV.
I can think of several reasons for used saddles on FleaBay. Someone tried it didn't like it, bought a bike that came with one and didn't want it, or is stripping out a bike for parts to sell.
Most if not all of my bikes have fenders which will keep the underside dry, and I goop the underside once a year with Proofhide, and the top every few months under normal use. I also carry a plastic bag in the seat bag just in case.
Aaron