An idea crossed my mind about how to avoid untrustworthy users more rapidly, how to save time with people who are very likely to not reply or who have bad feedbacks or responsiveness...
Why not creating a "score", public or not for each user, based on reponsiveness, last login, feedbacks or whatever is countable that would represent how trustworthy he is.
We could associate a colour with it, and the flag on the map would be filled with this colour, or people could use this score to sort members on the list page.
We would see for instance a member who signed up 2 years ago and has never hosted anyone and doesn't reply to messages in black on the map, and we would know at once that there is no point contacting this member.
Or we could display this score or something representing it on the profile page.
Actually it's kind of the same than forums user's ranks but based on multiple values and probably hidden to the user, so he couldn't try to rise his rank just for the sake of rising it.
And, as I see it, something colour related, quite discrete, without numbers like "your trustworthy score is 34,87/100" which doesn't make any sense.
What do you think ?