Should a classifieds website user be made to sign up before posting ads?

I am in the classifieds website business. I am struggling to find general consensus about the best way to design a user experience for being able to post ads on a classifieds site. Specifically, the site is http://www.buyagainbaby.com. But, this site follows the same pattern and architecture as the others I design, so ironing this out will help moving forward.

In order to both post and ad as well as contact an individual about their ads, should a user be made to sign up first?

There seem to be two schools of thought.

1) If I force the user to sign up you put security in place that maintains a certain level of integrity for content as well as accounts. Also, having a person sign up to contact a user allows for one to hide (or protect) the poster from receiving spam, which, is more prevalent when there is unfettered access to the 'contact this poster' form.

or

2) Allow anonymous users not only post but more importantly contact users about posts. I am finding that it is most annoying for authentic users to have to go through the extra steps to sign up just to be able to access the 'contact this user' form. If you have ever used craigslist, you may know how easy it is to interact with the site. At the same time, you know how frustrating it is to get so much spam.

The signup process is fill out name and email, and then verify via a link sent to your email address to activate the account - pretty standard stuff.

Thoughts? Thoughts on even a better way to find a balance here between ease of use and content / user integrity?

Any other thoughts on how the website could be more user friendly are greatly appreciated.