Kopenhagen, a bank transfer can take several business days even if you have the same bank. I would not, personally, want to accept a bank transfer for that reason. Immediate transfer of funds only happens in the movies 🙂 as a rule...one cannot expect it.

the funds will go from the sender's account, and they will have a receipt number. But it will take time for your bank to verify the money is available in their account, for you to get it.

As far as I know, the internet transfer cannot be reversed by the sender, but I would call your own bank beforehand to confirm that, they will be able to tell you for certain 🙂