Nihonto: expensive to buy, cheap to sell.
For all but the higher end blades (and lower end), one has to expect to take a hit on any re-sale. Especially if there is time pressure. I have come to accept this and thus have changed how large a collection I intended to have (it's going to be much smaller sword wise than I had planned a while ago). Now most would say "I have never lost money on a sword!" but keep in mind most also say that:
- they are ahead at the casino
- ahead on scratch tickets
- never lost money on real estate
- never lost in the stock market
There should be a zillion millionaires among us with these unwavering gains. It's weird there are not.
I have two swords; both top flight examples of their school or maker. Both top flight high end polish. Both with NBTHK papers. Both with top flight shirasaya and both with gold habaki. And I expect to lose 20% at a minimum and probably 30% or more if/when I should ever have to part with them. Sucks, but if you are going to be in this hobby, it's reality.