Help with the purchase

Hello, I’m new here and I need help with the decision! Would you like to chew me a slk either 200K or 230K. How can I find out as a non-specialist or the roof is really dense? I wanted to invest between 7 and 8 thousand euros, How is that with the mileage? Somehow I’m afraid of a mileage of over 70000km. Who can help me with the decision? Look forward to your answers Brigitte