Discount at the used car purchase SLK 280

Hello, now that I did a test drive with the SLK 200, I had to find out that the predictions have come true. I was a bit disappointed by the engine, somehow it runs a bit tough. I had an automatic, even in sports mode it was not really good. So I decided to buy a 280 from 2008, which is about 30,000 offered by the Mercedes dealer. Can anyone say how much discount there is still in there? I really only want 28. 000 spend, but the best offers are between 30 – 32,000,-. Is there a chance to get about 2 – 3,000 off cash? Or is that hopeless with Mercedes? Would be grateful for a tip and many thanks in advance.