All markets shift. Sometimes they are in the sellers favor, and sometimes in the buyers.
It's usually the general economy that causes the change, but not always. Often the market simply outran itself; sometimes it's over, or under, supply, sometimes it was nothing but hype to begin with, and sometimes it's just market sentiment and perception.
I bought a antique Persian carpet over thirty years ago. Paid $1,000.00. It ran up to about $15-17,000.00 in about five years. Now....about $2,500.00 if I'm lucky enough to even find a buyer. Reason for the change was that the US had an Iranian embargo on these items which initially drove the price up, then carpets from Iran began to flood the market through England killing the market. There's always a reason.
When, and if, another market shift occurs, the higher quality segment will usually recover first.
Good luck to all you collectors and owners.
J