With Wp Estate you can let visitors register for an account in the classic way (with the username and pass) but you could also let them login with their social media accounts on Facebook, Google Plus and Yahoo.
All you have to do is to go into Theme Options -> Social & Contact -> Social Accounts and fill up the forms.(see the help files about where you find all those details). Once you did that your visitors can login (and publish listings) using their social media accounts.
Sometimes your website may be the target of spammers and they will try to create accounts using some premade scripts. To avoid this threat we added the reCaptcha functionality (can be turned on/off in Theme Options -> Advanced -> reCaptcha Settings)
After you put this module to on your visitors will see a “captcha form” on registration window and you will prevent the creation of fake accounts.