What affects my car's value?

Lots of things, really. Here are the main ones:

1. Make and model - some cars are just more desirable than others
2. Age - newer cars are generally worth more
3. Mileage - lower mileage usually means better value
4. Condition - bodywork, interior, and mechanical condition all matter
5. Service history - full service history adds value
6. MOT length - more months left on the MOT helps
7. Number of previous owners - fewer is generally better
8. Colour - yes, really! Silver, black, white, and grey tend to be more popular
9. Modifications - can increase or decrease value depending on what they are
10. Market demand - some cars are just hot property right now