In our efforts to fight scammers we have for a while now required that users be registered for a minimum of 3 days before they can contact an advertiser via our classifieds. We've now expanded this functionality to enable advertisers to choose how long a user need to have been registered before he/she can be contacted by that person.
The minimum default remains set at 3 days. On the form where you post a new ad there is now a "Buyer Days Registered" option that can be set to:
3 - Default Minimum 7 - One Week 14 - Two Weeks 30 - One Month 60 - Two Months 186 - Six Months 365 - One Year
The higher you set your days required number, them more users (including some bona fide buyers) will not be able to contact you, but the lower the likelihood of being contacted by a possible scammer. Scammers typically register usernames and hope to use it immediately to contact sellers. They seldom register and come back after months and log in again under the old username.
Manage your own risk. You choose what you're comfortable with and set the cut-off.