Never sell domains in pairs. Unless it's an offer you can't refuse.
I think owning bookends is a good thing for re-sale.
The end users are clueless about type-in and traffic bleed. I think you need to educate them when pitching the domains. Search volume is also relevant data.I sometimes contact the owners of the singular and they say, "Sorry but I'm not interested in that domain at this time." which makes absolutely no sense to me. Just recently, I contacted someone who owns the singular and I own the plural as a developed site; they weren't interested and didn't even ask what may price was. The plural gets more searches as it is physical product. Go figure...
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