Your missing a few important points though:
- If the seller bought it new, they paid circa £30k, not £20k. So selling at £10k is a £20k hit compared to the £10k hit you mention when quoting new zeds at £20k. Thats 33% of the original value compared to the 50% of the new value you want them to sell for. If they sell for 50% of what they paid new, then you'd be forking out £15k.
- Not many people actually know/knew that you can/could get zeds for £20k. There was a very limited supply and they went very quickly IIRC.
- If you can't get a UK car for less than £10k, thats because the market hasn't taken them to that point yet no matter how much you try to batter down their prices.
- Would you be quoting Parkers guide if they said an 04 GT was worth £12k?