Looking for certified used car dealerships

Just look for dealerships of those companies and contact them to ask if they also sell used cars. Most probably do since they need to get rid of trade-ins. But one can usually find better deals elsewhere. There are a number of good German websites for used cars like Mobile.de. The advantage of buying from a dealer in Germany is that they have to give a 1-year guarantee on used cars, while private people don't. Unfortunately, there are some loopholes in such guarantees. The other thing with dealerships is that they tend to charge a lot but are not necessarily be more reliable. If one has a problem with a used car bought from a dealership, don't assume they will solve the problem without hassle. Excuses as to why they don't really need to cover a problem or lack of effort to really fix things properly are not uncommon. Been there, done that.