Is it too much to ask to live in my sister's apartment for a month?

I would like to move to Berlin, and I wanted to see it there. How life is there. My sister wants to sublet the apartment for a month anyway. So I thought, I could move in there, would pay the rent too. Then I asked her if she could rent it to me. Then she said: a buddy pays 800 euro and I could almost buy my laptop. Then I: I'll buy you the laptop. Then she said, groaning and annoyed: why are you causing me such stress, then come on. I don't want to anymore. Was that asking too much of me?

"Then I asked her if she could rent it to me"

Since you didn't expect to get the apartment for nothing: no, it wasn't asking too much.

And should she let her buddy hang in the air now? He probably already relied on getting the apartment. Now your sister is sitting between the chairs…

No, basically it's not too much to ask of your sister - especially since you wanted to pay for it too. But if something was already agreed, then you can understand that nobody breaks out in enthusiasm.

It is certainly not asking too much. But she wants to sublet her apartment and can therefore decide for herself who will subtenant.

A buddy pays 800 euro and I could almost buy my laptop.

The difference could be - renting out to a third party - without the consent of the landlord = the landlord could terminate…

It looks a little different when taking in a relative.

Otherwise… Accommodations are likely to be cheaper than usual at the moment (due to a lack of demand due to Corona) … So you can also go exploring Berlin / looking for an apartment.

Your insistence and willingness to discuss is a bit asked - here too.