When I first saw the sale notice, I purchased a number of books, each unique. I saw it as an opportunity to get the basic skinny on a number of places for future trips. In actual fact, the attractive thing about RS Guidebooks is that they are updated every year, and the information is fresh and (usually) accurate.
There will be no European travel for me this year, and probably not in 2021, either, unless our COVID/death numbers start to decline dramatically, so the immediate value of the guidebooks is probably close to the $5 I paid for each of them. Timely information is precious; stale information is frustrating. Still, the books provide basic guidelines and hints for travel, even if an updated book would be preferable.
Perhaps people who purchased a large number of certain books for resale (if that is the case) will make a small profit in the short term, but my goal was to amass a small library of books on places I wanted to visit. My girlfriend is angry about my purchase, and I have promised her that I will get rid of earlier editions of books I already have to make room for the new arrivals.
With that said, on my last trip to Italy (2019) and to Paris (March, 2020), I found the Internet more useful in providing me with immediate and topical information about hotels, museums, restaurants, and other information about places of interest than any guidebook. I think things are changing in the world of European travel.