I only put an ad on craig's list once - don't have much to sell.
But I did learn this. If you're an occasional seller, set up a BRAND NEW Yahoo, Google, (or whatever) email address for your ad. They are FREE. That way, you never have to worry about all the spam coming in to your good email address once your done selling your item. Let the temp take the brunt of it.
Use your regular email address and you will be getting spammed forever.