What products do you think people generally sell for less than what they are worth when they are used? I have found the main things to be laptops and phones, probably because so many people get theirs on a plan/ upgrade every year so never consider buying a used one? For phones I can buy a high quality 1-2 year old phone for $100-$200 when a decent mid range one would be 500ish and for laptops I bought a lenovo x220 for under $200 which is a great laptop that probably still beats a lot of new laptops performance wise.
Ah, a subject near and dear to my heart.
I have two schools of thought: First, something is undervalued due to a very steep depreciation curve, which truly isn't warranted. This is the "A car loses 30% when you drive it off the lot" phenomenon. Things like hiking boots with 90% of life left can often be found for 10% of new price, high end clothing (anything cashmere, made in Italy, a few premium brands like Burberry, Zegna, etc - ones I literally never heard of until I saw high quality materials but didn't know the name so I researched). Although you can get these things at 70-90% off new, that's probably a fair price. These are generally things I buy for personal use.
The second is undervalued, due to being obscure, and even though used, will sell for much more on a market once the right buyer comes along - but get grouped along with the other low end stuff there. These are things like tools, optics, knives, bikes and books. Far more work and knowledge required here, as it requires knowing intricacies like the difference in worth between various editions of specific books, identifying high vs low end models of derailures on bikes, and having the wherewithal to spot that needle in the haystack of 5,000. These are things I will buy, even with out an immediate specific need (although at least a potential future use), and can generally be confident that even if I don't use it, I likely won't lose money. This is where as Warren Buffett likes to talk about 'multiple margins of safety' come in.
Electronics are very finicky I find. For whatever reason like the blades of tools, they seem to degrade over the years, even though I don't do anything different than I did 20 years ago with them, and computers have supposedly gotten faster. Web browsing, book flights, movies and email. Yet I have a computer from 2002 running XP that takes 15 minutes just to start up even after several hard reinstalls.