Smaug

I am not the wonderful source of information that Panda is so I can only give you general, common sense advice, which should not be taken as advice anyway because I am not a lawyer.   You can contest the decisions of German authorities directly with them. If you don't within a certain deadline these decisions become final. If you contest and you still disagree with the the new answer you can of course take the Jugendamt to court. Naturally, before you do any of this you need to work out what it is that the Jugendamt has done wrong and appeal that (it needs to be a lot more specific than "they have acted very badly"). Everything has to be backed up by laws (statute or precedent). If you post details here maybe someone can comment on your case.  

Thanks for the tip @BradinBayern. I am hardly ever in Munich but next time I'll try Condesa.

  I have to laugh at your post. You are right, and I know Taco Bell is crap, but I'd welcome them. Cheap and cheerful Pseudomexican is a great alternative to döner or bratwurst. And do you really think the average döner joint has better health standards than Taco Bell?

  There's been a Chipotle in Frankfurt for a while. If the food there is the same as in the London branches it should be pretty decent Tex-Mex, but I have never been to it to test this, although often work just a five minute walk from it. I might try it today and report!   Mexican food tends to be a disappointment. There are some okay options in Frankfurt but nothing spectacular really: skimpy on the fresh ingredients, expensive...

Public transport is great in Leipzig. It's also a very nice town.    

Some German ATMs also allow you to do a transfer even if you don't have online banking. Instead of putting the filled out slip in the box you enter all the information into the terminal after after accreditation with your bank card and PIN and off it goes. 

For all you know he could have fixed the damage himself.   The threat to contact a lawyer is just an empty threat. If you don't have an invoice, what is there to pay? I'd also follow SP's advice. You only pay bills in YOUR name.

  No, it isn't worth it. Are you saying the current tentant is still encouraging you to go for it? Don't listen to her Her options are to give up the flat or find a sucker to sublet from her. It's understandable she doesn't want to give up the flat given the market for accommodation in Berlin (she knows she's going to get less for the same money when she comes back in year) so she's trying to find someone to pay the rent for her and hoping that the landlord doesn't get wind of it. What happens if he does? He'll be perfectly entitled to rescind the contract with her and kick you out.

  No, you are not allowed to LIVE there. The owner has explicitly said "NO".

    I've bolded the key sentence in this paragraph.   The first part says that the "flat-giver" is obligated to cooperate  in the registration.   The second bold part says that YOU are obligated to tell the authorities immediately if the landlord refuses to cooperate, as it is your case.

I've often used my credit card to pay from friends' airfares. In fact, if memory serves, Lufthansa's and BA's website booking mechanisms explicity guides you on how to buy a ticket for someone else: family member, boss, friend, stranger... who's to say?

  You need to go to the Bürgeramt and tell them you want to register at your new address. That's your legal duty. The bold  sentence is fantastic news! Just take it to the Bürgeramt (do you have a copy? could you ask for one?) when you register and give it to them. They'll love it. It's basically a written confession of the owner intending to break the law by putting a deliberate impediment to what you must do by law.    

  I am also very flexible with my tenants (let them give notice via email, even one month is okay...). When I read the regular posts on TT about landlords obsessed with screwing up their tenants my blood curdles. That's their blooming problem? Maybe it's that I've been a landlord for only a short time and I haven't had problem tenants yet and that's why I am still so nice.

After a guest has stayed longer than six weeks, he or she could be considered to reside at the flat and the landlord needs to give his permission. A few days is absolutely no problem. Sometimes landlords don't allow overnight guests, or try to ban guests of the tenants opposite gender. These prescriptions should be ignored. The tenant has the right to enjoy the property she's paying for and is allowed to have guests as far as they remain guests (they don't actually move indefinitely). You don't have to tell the owner, in fact, you shouldn't. It's none of his business.

It's not worth it in my view. To earn that kind of money on the side you are better off doing a minijob, which you don't even have to mention in your tax return. If you are a trader you have to keep books and calculate income tax and trading tax, even if your turnover is not high enough to trigger a VAT requirement. A royal pain in the ass. The income tax would depend on your other income.