That seems quite high to me for an almost 5 year old used machine, because yes they depreciate. I'd be thinking more like 10k. However, to the owners they know it's lightly/barely used and people typically over-estimate the value of their own possessions.
Here's some national listings for used machines through one of my local-to-me long arm quilters:
https://longarmuniversity.com/MachinesForSale.html#M4S