Companies such as Europcar, Avis, and Hertz have literally hundreds of offices throughout Germany. However, since there is a 20% surcharge on rentals commencing at German airports and rail stations you will probably want to pickup your car at a city office. In smaller towns the rental car franchisee of an international rental company may be in family-run service station/convenience store with a tiny selection or cars...and you might have to wait while the owner pumps gas or sells a liter of milk.
Though a rental car in Germany will cost the same in a small town as in big cities like Frankfurt, Munich, Berlin and Hamburg, you’ll get more knowledgeable service and a better selection of vehicles in metropolitan areas. For example, even though you have a confirmed booking for an automatic transmission, complaints about promised automatics not being available invariably come from smaller towns and not from major cities. Insurance can be another problem at a small-town rental counter that sees few North American customers. Since their credit cards rarely provide collision and theft coverage, Europeans routinely purchase the optional insurance. Thus rental agents unused to dealing with North American often assume they, too, want the optional coverage. If you aren't careful when signing the rental contract you could come home a substantial, unintended charge for insurance on your credit card statement.