Hi Robin, should you get to read this. I enjoyed your article in SOS.
I’ve seen, but not used, something similar on Music Xray.
They seem to be more targeted by genre, end users solicit specific requests e.g. country/rock song for a female artist. Some were happy to receive demos others wanted fully mastered tracks that they could then put their artist onto once accepted and your guide vocals removed.
You could pay for your appraisals by doing the same for other artists.
It’s a bit disconcerting that you had such contradictory responses, but maybe as you say musical taste is wildly subjective.
It makes you wonder if some of the paid for listeners have given your song a good listen though, when one opinion says the vocal is buried and the next that it’s crystal clear.
I wonder if there’s some feedback mechanism to get rid of those people that just cut and paste a few stock phrases into their critique and make quite a bit of money.