To estimate the price of the 2018 BMW 520 M Sport with 300,000 km mileage, I first looked at the selling prices of similar cars. The most relevant data point is a 2018 BMW 520 M Sport with 160,000 km sold for AED 69,000 on 2024-02-22. Given the higher mileage of the target car, I adjusted the price downwards. Next, I reviewed listed prices of similar cars. A 2018 BMW 520 M Sport with 160,000 km was listed for AED 72,000, and another with 159,000 km was listed for AED 84,500. Considering the higher mileage of the target car, I further adjusted the price downwards. Finally, I considered the general depreciation trend and the condition of the car to arrive at a fair market price estimate.