How to trigger an email for a buyer or seller who has not performed any activity for 30 days or more?
Finally i got the answer here:
https://www.drupal.org/project/inactive_user

The inactive_user module provides Drupal administrators with a way to automatically manage inactive user accounts. This module has two goals: to help keep users coming back to your site by reminding them when they've been away for a configurable period of time, and to cleanup unused accounts.

And another possible solution is:
Using rules for more advanced functionality would involve something similar to the following

Create a new Rule Set that passes the User and (possibly) a Date argument

Add a Check a truth value condition that verifies something like [user:user-last-login-raw] + 2592000 &lt; [user:date-in-tz] (2592000 is 30 days in seconds)

Add a Send a mail to a user action

Save that rule set and then do the following:

Create a new triggered rule for User has logged out event
Add a Schedule "your rule set" action and pass +30 days as the Scheduled evaluation date