Not much point to using a variation listing.

You get 250,000 free listings, so use them.

I would also get peeved if I saw a variation listing for books.

Also, re your sets for sale, if I was missing one or two books for my collection, I'm not going to buy the whole set.

BTW one of your listings for Dr Seuss' books quotes both Free Postage and a postage cost   ???