If you are referring to responding to an ad on craigslist, then I would recommend you create your "spam" email address, e.g., sign up for a free yahoo or gmail account that's primary purpose is to absorb the spam.
So you respond to the ad from your spam account, then check to see if you get a valid response. You can later tell the prospective client that you have a new email address and use your everyday account.
Fake ads to get responders' details or scraping the classified site?
I keep a disposable address for use with strangers and a private address that only gets revealed to those who I trust.
There isn't much the site owner can do filter scammers in advance. A reporting mechanism for problems seems like a good idea but it could also encourage users to try and make you a party to disputes. You could ban the use of disposable addresses by advertisers but legit advertisers will want to keep their "real" addresses out of the public domain for much the same reasons.
Scraping - obfuscate addresses or use contact forms, maybe with a captcha.
My site allows the person creating the listing to publish a phone number. This is just like any classifieds you might have found in the newspaper years ago. This phone number is available to anyone visiting the site.
To contact a person via email, you must be registered.
The email is then sent to the seller from my website.
The buyer only sees the sellers email address after they have replied to the email.
Things such as someone contacting the seller via email through the system and pretending to be interested in the item for sale. When the seller responds, the scammer has the seller's email address and uses it for whatever. I see this constantly on craigslist.
I'm planning to use e-classifieds by Hagen Software and was wondering if there is any way to stop this.