How to trigger an email for a buyer or seller who has not performed any activity for 30 days or more? Is there any way to trigger an email for any buyer or seller who have not had any activity for 30 days or something like that.

Also
Sending reminders to users that haven't logged in for 30 days.

Unpublishing content after user has not logged in for 30 days.

Deactivate accounts after user has not logged in for 30 days.
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