First of all, the form and content of your feedback are free. Your comments need to be at least 15-word long.
Each curator / pro joining Groover has to approve the Guidelines for Groover Curators. It is important that you try to put yourself in the shoes of the artists you're giving feedback to. What's important to them is to:
Get your view on their track, obtain a clear decision regarding you sharing them or not / getting in touch with them or not
Get constructive advice to improve their work and/or their strategy
Understand why you liked / didn't like - and especially in that case - their track
You can find the guidelines detailed below: