I agree with what you guys are saying, HOWEVER, I've seen at least 10 ads where Mods have stepped in and said "either it is for sale, for trade, or for both. You can't list something for trade and then say 'send me a cash offer.'
If you are accepting cash, then you are supposed to post a cash value. That is in the rules we all agreed to.
Just putting "OBO cash, shoot me an offer" is, in and of itself, against those rules.
But I definitely hear you on the rest of the postings.