[makeapoint]

They don't need anyone to trust them and they have nothing to gain from decrypting your files.

They may be a 14 year old kid who ran some kit that somebody else made. If they collect $50 from 25 people, they will be stoked.

Or they may be a sophisticated criminal organization that want to built long term viability.

It's impossible to know which it is. But it is guaranteed that they are criminal and inherently untrustworthy. It is also guaranteed that any money you pay will finance the next wave of more sophisticated malware.

So, no, you cannot trust them to do good. You can trust them to do bad. Now, make your microeconimic choice.