Is bandcamp watermark free?

I don't know. It was a genuine question.

My hunch; no way Apple and Amazon will not watermark. But that is just based on behavioral inference, not on knowledge or data.

Apple does indeed include the original purchaser in the MPEG-4 metadata. I have no idea whether or not they also do any kind of more advanced watermarking of the actual audio data itself.

No, not for a while. As I understand it they didn't have one at first but after some asshole used it as a backup (since they let anyone upload "music") and made a blog post about it they added one. Quite possibly they wanted to anyway and it was just a convenient excuse.

Do you have a link?

Thanks for asking, because it turns out I was wrong :(. I should know better than to rely on my memory these days. If you download the same FLAC file twice it won't be the same (possibly unless the two downloads are within a few days) but I just checked and they do decode to the same WAV. I haven't checked multiple accounts but when trying to find the article I thought I remembered I found someone saying they had checked and found them to be the same (not that long ago). I'm not sure if the FLAC or other specific file downloads are ever exactly the same between accounts, possibly not and they record the generation timestamp or such, but it seems the audio itself is not watermarked.

The backup thing did happen, though:

https://medium.com/@__Tux/using-bandcamp-as-a-backup-solutio...

What is the problem with watermarks?

I actually love watermarks as a solution for DRM-Free media, because they make illegal sharing more cumbersome but don't impede legitimate customers (at least in any way I can think of). In fact, I kind of feel like watermarks add value, lending an authenticity to my purchase which a pirated copy wouldn't have.