Of course you always have to assume worst on a purchase but you can reduce the degree of horrors you'll experience by going after the cleanest, best maintained example you can get.

Tell me, how much did you pay for yours and how many miles did it have at the time, if you're ok with disclosing it? Thanks.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver