There could be many reasons for a cut-price sale from a seriously defective car, something fishy in the title/history to simply needing a prompt sale. Do the appropriate checks for theft, w/off, debts etc. and perhaps have a look at it if it still seems OK. If you are worried about some aspect of the car either walk away or have it inspected. Could it be just about due for tyres, brakes, rego, timing belt, clutch plus a major service??? You might win the Quinella or Trifecta!
....it is a Mercedes dealer.
Which could mean they took it as a trade for more than any wholesaler would offer and thought they'd have a go themselves, but have now decided to quit it. It's probably OK, just not the sort of car that dealer wants to keep. Friends bought one new and it's turned out to be an excellent car for them ... well apart from the depreciation aspect!