hearing clicking in engine at idle

Yes, I would walk away. The ticking could be many things, none of which are good. Best case, these are high cost vehicles to maintain, so why buy 1 that has a known problem.

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The ticking sounds like a engine lifter the first thing you need to check is if the owner has been using synthetic oil the German cars have to have it. If they are using synthetic I would have them do a oil change, Ive found that when the oil level is low the lifters dont function correctly and you get that ticking noise