I sell quite a bit on CL, Usually all contact by email, its how I want it. I ignore the "Is your item still for sale" emails" the buyers who seem high maintainance, asking a lot of me as a seller (meeting, shipping, excessive questions that are answered in ad) pushy buyers (call me, take $XXX its a good deal, only half of what you are asking), these get pushed to the back and rarely answered. Emails of some of my easiest sales have been fished from the spam bin.
I believe in a want ad etiqutte that many people dont have. A brief outline of it is,

First contact introduces and expresses interest and asks a couple of questions about the item that can not be answered by reading the ad, even a remeasure of frame as its often done so badly and maybe possible meet times.

Followed by seller answering said questions and choosing or offer possible meet times.

Second buyer email confirms interest and meet.

Seller email gives address of meet and phone # for last minute changes.

Meet, deal done or not. If not I often ask what exactly they are looking for as I do get bikes in frequently and call or email them if I get it or show another bike.

The big no nos to me are the throwing out an offer in the first email sight unseen, unreasonable requests such as meet me halfway (thats mine to offer)
don't flake on meetings or if you do give notice as soon as possible.

Typing this I'm suprised I sell anything but it work for me