A car's market value is not a fixed figure but the result of supply and demand. Make, model, year, mileage, equipment and condition all matter – as do the current market situation and your region.
Start with comparative research: look for identical or similar vehicles with comparable mileage and equipment. The average of these listings gives a realistic range. Keep in mind that asking prices are usually a little above the actual selling price.
Value is increased by a full service history, few previous owners, sought-after equipment and a well-kept condition. It is reduced by accident damage, heavy wear, pending repairs and an expiring roadworthiness test.
Also use a professional price assessment, like the one built into mobilsale24.de. It automatically compares your vehicle with the market and shows whether your price is low, fair or too high.