Just my two cents.....
In all the comments and OP's post I miss something vital......basically the procedure described in regards to a possible Betreibung are correct.
But, should this happen and a Betreibung is filed against you, then you have 10 days time after receiving that letter to file an objection (Rechtsvorschlag erheben), you have to do this either in writing by registered mail or directly at the Betreibungsamt (office des poursuites).
If this is lodged in time at the Betreibungsamt, the whole procedure gets stopped and it is up to the creditor to prove that his claim is correct and you are indeed in his debt.
If the creditor fails to provide the proofs and you maintain to dispute it, there won't be any Betreibung at all and no entry in the debtors register (Betreibungsregister).
However, if the creditor can prove you are in his debt and you still deny this, then it is most commonly a case for court......
Also, if a document needs to be certified after translation, it is best to seek the help of a Notary.....
Right, but you're missing that the creditor is allowed to simply do nothing after a Rechtsvorschlag. No proofs, no courts, nothing.
Then the Betreibung stays logged in the register as disputed and will haunt any your potential future landlords for next 5 years. This is what many people are afraid of, that they won't get any apartments if the Beitreingsauskunft casts any shadow of a doubt on their creditworthiness.
You can get it cleansed by bringing the matter to the court yourself, but it takes time and some money upfront for the court costs, which you'd hopefully get back (much) later if you win.
The problem is people writing negative reviews are using words which can be potentially harmful in a legal way. It is seldom the pure recount of what happened but all the negative feelings and judgments which are made. Words such as "crook", "layer", "fraud", "thief" and advice to others "stay away", "do not go there", "the worst place you can find" which can backfire. The line between an opinion and slander can be very thin and you will easily cross it when you are agitated und upset after a very bad experience.