Bought a rooted phone =/

Hi all!! I just recently bought a rooted phone, I didn't know it was rooted until I looked at it closely. Apparently the last person done a few things with it and now I'm unable to access the playstore, it gives me the message "Can't establish a reliable connection to the server. This could be a temporary problem or your Android device may not be provisioned for data services. If it continues, call Customer Care." I don't want to mess it up anymore than it already is. Is there any help for me? I have a Samsung Galaxy S4 model # sgh- I337.