Two other sites to check for 2nd hand bikes:

MotoScout24

SwissMotos

Although from what I've seen Motorradhandel is the best.

However, not all dealers advertise on there/or are necessarily up to date. If you know what you want, find your local dealers from the manufacturers' websites and pop down and have a look what they've got in the shop or give them a call. I just bought a bike a couple of weeks ago, exactly what we were looking for and at my local dealer, but he hadn't even advertised it on his website let alone anywhere else - it was only because we stopped by the shop that we saw it