I'm not sure whether anyone is familiar with giving feedback on Airbnb and/ or Couchsurfing, but I think it's pretty good, and maybe something that Warmshowers should adopt? On these sites' platforms, after you've hosted someone you get an email to give feedback. You have to give the feedback within a certain timeframe for it to be verified. You also can't see the host of guests feedback until after the timeframe has passed, or until you've also provided feedback.
I hope that makes sense (I probably didn't explain is very well). I thought maybe that could improve the Warmshowers feedback? I think it would make the feedback more true and creditable.
Just a suggestion :)