As I say I found Glass's spot on for the Celica. It even listed what criteria they use for things like Excellent condition, which includes things like 4 nearly new tyres. My Celica was in really good condition but to bring it up to 'Excellent' would have been £500 which was the difference in value between the two rating.
I got £8500 the same value in Glass's against a new Cupra. I managed to track what happened to the car after. Basically the SEAT dealer auctioned it and another dealer (big nearly new car specialist) bought it and tried to retail it for £9995 this gradually dropped to £8995, which is when I suspect they sold it and it looks to have been taxed since so I presume a customer bought it.
I'm pretty certain that somewhere along the line somebody took an unexpected hit on the value of that car.
The Parkers value was way out, they reckoned £9200 in part ex and over £10,000 retail, but just shows that even a large dealer couldn't get that sort of money for it.