As a serial market watcher, I've lost track of the number of classic/specialist cars that have been privately advertised at somewhat optimistic prices.
Unfortunately, they often end up at auction where the car doesn't achieve it's estimate and the owner, who by now is thoroughly disillusioned, accepts an offer far less than they would have accepted from a private buyer in the first place.
My advice would be to recognise that the market is not what it was and advertise for a realistic price in the first instance.
I've watched two specialist cars (not Morgans), that were known to me, go through exactly that pattern. In both cases they started off at £40k plus and were eventually sold at auction below £30k.