Poor account management at home bank, application at another bank?

Search for "Purchase on account not possible" and read through it.

I have done that. Creditreform also seems to collect data on private individuals, yes. But I never buy anything on account and I have not seen any reference to data collection regarding online gambling.
Thank you anyway for your response. I might also request information there to find out if and what is stored about me.

Did you have returned direct debits? Many? Did account transactions take place through third countries (Andora, Cayman, Cyprus, etc.)?

I only have concerns that after opening an account with another bank and having a good account management there for several years, a credit application will prompt the new bank to request a bank reference from my old bank. Is that realistic if the bank account has already been closed for several years by then and I can already look back on a multi-year relationship with the new bank?

I think that is unlikely. In Germany, we also have something like data protection. What they request, you have to sign beforehand. In our case, it was only the Schufa. If you want to know what Schufa knows about you, you can request a report once a year under paragraph schlagmichtot, then they have to send you your complete data set.

I was thinking of keeping the account at the old bank "clean" for at least 12 months before switching and then switching so that it still looked good before obtaining a bank reference. Does all this make sense?

No. You are worrying way too much, I really can’t quite understand the fear? Either you are hiding something here, or you yourself don’t believe the vast majority of forum members who are all telling you the same thing here.

I think that having good trust with the main bank will possibly help me later if I apply at another bank and they (though this apparently doesn’t seem usual with private individuals) request a bank reference. At least in this way I have a multi-year main bank relationship with good account management.

I don’t believe that. My husband financed his first house (with me), he was the main earner, and he had only been in Germany for about 2 years, and our account was at a direct bank. They can request relatively little there, and his Schufa was probably as clean as it could be simply because they hadn’t had 20 years to let the data monster work its way through. It still worked.

Did you have chargebacks? Many? Were there account movements through third countries (Andorra, Cayman, Cyprus, etc.)?

Yes, I had one this year. And there were some money movements, so money laundering was suspected. I then just told them it was online poker and apparently that was that. But as I said, I think it all cast a very bad light on me and I was probably classified as a high-risk customer by them. As I said, I immediately stopped that nonsense and will never do it again. I’m really scared and don’t quite know what’s best now. I’ve always tried to push myself in life and now see my future threatened because of this. Maybe I’m already in some database due to the suspicion of money laundering. I was so careless, it’s just stupid.

I requested my Schufa report and it only shows my checking account. I have no other contracts, I even canceled my credit card back then. Schufa score is 98.8%. I don't think it will fail because of my Schufa, even though the banks apparently look at the industry scores and not the base score anyway.

I requested my Schufa report and there’s nothing on it except my checking account. I have no other contracts, I even canceled my credit card back then. Schufa score is 98.8%. I don’t think it will fail because of my Schufa, even though banks apparently look at the branch scores and not the base score anyway.

I think that all sounds rock solid. I don’t know why you absolutely want to change banks. I can’t imagine that any of your “baggage” will trip you up. Many of us committed some account sins in our youth or student days. But if something like that were to catch up with you for life, probably only 20% of people would be able to get a mortgage. A bank even once closed an account of mine back in my carefree student days. I didn’t use it anymore, barely took care of mail, and it stood for ages with a small negative balance, and eventually they closed it, but I still owed them the money. Definitely about a decade later, when I got my life in order, I went into a branch with the old statements/letters and the cash and paid it off. The employee was a bit overwhelmed because he didn’t even know how to post it. :D But in the end, with some help, it worked out. Anyway – I think a bank-closed account would probably be more dramatic for a mortgage than a bit of online poker and a few returned direct debits. And after that, no one even batted an eye here.