A junker, as I would classify it in Germany....is typically a car that you pay between 500 and 1500 Euro for. It has a time-limit of sorts....that you hope it lasts for twelve months, but if you can get two years out of it....great. So this is my advice on this option.
First, get it into your head that you are paying a very low price for a almost dead car, and you really are doing it just as a band-aide approach to your transportation needs. You accept risks, and you simply want to save money in the end.
Second, never buy just based on the price. It has to have some presence of lasting. If the vehicle inspection was just done.....fine. If the inspection was ten months ago.....you might want to ask a lot of questions. You have to figure the car will be at least twelve years old, have some rust, and have a funny smell inside. Smoke coming out the tail-pipe? Walk away. Leaking oil? Walk away.
Third, you ought to have a local mechanic that you trust.....and just have the car looked at for two minutes by this guy on the lift. He'll spot any serious rust (it's not doors or side of the car you really need to worry about). He'll tell you about oil leaks. If he says nothing obvious, then you might have a pretty good deal.
Fourth, rust on German cars is fairly common after fifteen years. So don't get excited about that. You typically spot it on the back window area, or around the doors....occasionally, the fender. It snows in Germany, and they use a fair amount of salt. They will tell you that newer vehicles have better protective coating than thirty years ago, which is true. Back in 1977....a car would typically be rusted out by twenty years of use.
Fifth, from the top down.....Mercedes and Audi cars tend to last longer and stay in better shape. So a fourteen year old Mercedes might actually be in great shape for its age but down in the junker status. BMW and Volkswagen....probably at the second level. BMWs always have some weird electrical issue after about eight to ten years.....while they look great and avoid rust for some odd reason. The VW? Well.....they run forever, and parts never appear to be a problem.....but if they started out at 20k Euro brand new....figure they hit the 1,500 Euro level by the tenth year. Opel, French cars, Italian cars, and British cars.....well....a lesser choice for the junker. The thing about Opels is always the body and rust....it's cheaper metal and they all have some element of rust by twelve years. I would probably shy away from any Italian car that is over fifteen years old. A tip on the Audi brand.....they all burn oil from day one.....typically one can of oil every four to six months....just accept that as part of the deal for an Audi (keeping a can of oil in the trunk).
Sixth, don't worry about the car seats, the carpet, or the interior. Remember, this is purely for getting to work and nothing else.
Seventh, a fancy Mercedes 300S series? Well....it could be a junker, but here's the thing. It had a lot of special extras. These tend to break. How much are you willing to pay per year? If you are a true junker enthusiast.....then your general limit of maintenance cost is one thousand Euro per year. This means you ought to repair/maintain the battery, the lights, the muffler, the starter, the generator, the alternator, the brake-pads and the wipers. Transmission issues? Forget it and junk it. Got issues with burning oil? Count the days and figure if you get thirty to forty more days of use....it'll be worth it, and you just junk it. Don't even think about a two thousand Euro repair job.
Eighth, don't put huge expectations on long travel with a junker. Limit your travels to just the local region. Dependability to drive from Frankfurt to Munich is something you don't want to consider with a junker.
Ninth, cracks on the window. It's an interesting topic. You can have a small crack on the window and get by via the inspection system. A crack longer than your hand? Forget about passing. The smaller spider-like cracks? A local glass shop can do some work and maybe fix it enough to pass inspection for roughly 50-80 Euro. New window? Well.....if you want to negotiate with the glass guy....you might get a special deal for 250 Euro but typically....it's a 400-500 Euro deal if insurance was involved.
Tenth, don't worry about fuel efficiency. Junkers aren't important when it comes down to fuel. Figure you get 20 mpg with just about any standard 4-cylinder German car. That's acceptable.
My best junker story? I worked with a guy who paid roughly $1,500 for his French Renault which was around twelve years old. He put some seat covering onto the seats (they were crap), a nice smelly device (mildew was an issue), and then changed the oil faithfully every four thousand miles. The car lasted five years. He never drove it faster than 100 kph and actually washed it once a month. Now, he never drove more than 700 miles a month....stayed local....and typically did most repairs himself. He'd openly brag that he never spent more than $800 a year on total maintenance. He sold the car for $1000 as he left Germany at the end of five years. That was a five-star junker.
My worst junker story? I knew a guy who'd found a terrific Porsche 914 from around the mid-1970s. It was around fifteen years old at that point, and the engine was totally shot. He picked up the car for roughly $1k. He spent around $6k by the end....to put a brand-new engine into the car. Six months later, there was a $2k deal to totally rebuild the brake system. A month or two later....there was $1k for a muffler job. After two years, he'd put almost $12k into the car to keep it operational. The thing was....it did have some rust, and the market value at the end just didn't relate to the $12k and the $1k original price. He sat there....trying to sell it for a fairly decent price, but no one was going to pay for all the repairs he'd done. So he essentially lost most of his investment in the car at the end.
So, if you get to Germany and make this decision about a junker.....just remember, this isn't a car that you want to get attached to or want to put big cash to keep it running. Yeah, you might be able to get that Mercedes 300S that you always dreamed of.....but don't put a lot of faith in a fifteen-year old car.