How to set up a trial-based account for users on an ubercart site? I want to set up a trial based account for an user who will sell his products. After he paid the payment, i will upgrade him to role seller.

Until his role is upgraded to role seller, i don't want to show add to cart button for the added products.

First of all how can i differentiate it to be a trail site for example. 30days until he pays, if not i want the role to be expired. How can i do it. Any suggestions will be helpful?
Create 2 user roles: Trial Seller and Seller. 
Create a Rule. 


Event: "Drupal is initializing"
Condition: User has role -> "Trial seller"
Action: php that will hide (disable) the add to cart button. You have to use the hook_form_alter function (or similar) like described here: https://drupal.org/node/773312#comment-7425408



The second question is another seperate task.


Create a Rule:


Event: "Drupal is initializing" 
Conditions: User is of role "Trial Seller" AND not "Seller" AND php "(Current_date_time - Account_Created_Date) > 30*24*60*60" (to see if the time from the user account date until now is more than 30 days, time in seconds) AND he has paid
Action: Remove user role -> "Trial Seller"



There is also the module Role_Expire that may help you.