Those places are not all that great and quite expensive considering they are not regular mechanics. They check the on-board diagnostic (car's sensors) for any errors (which you'll know if there's an error via the check engine light). They also look at emissions to see if there's anything wrong. They check the body, but if the work was done well, it's very hard to know if it was in an accident before. They do a test drive but can not really tell you wants wrong unless you take it apart.

If you want to check the emissions and look for some body damage, you can take it for technical inspection (before you renew the car registration).

GPS for German Auto is somewhere here (may be 1 block before or after, but this side of Salwa):
25.237253,51.452428