I am creating this to explain the 12-hour bumping rule, so that you as a seller will know when to bump, and you as a reporter will know when to report and when not to report a thread.

Before we proceed, let it be known to all that a BUMP is not just a reply with the words "bump for today" or "up up up!".
Every reply posted in a thread is considered a bump, simply because it makes the thread climb on top of the list.
I hope that I have made this clear, that even if you say "PM sent, check your inbox", it's already bumping your thread to the top position, whether you did it on purpose or not.

By the way, the forum has a notification system for Private Messages, you don't have to tell the buyer that you sent him a PM, he will know.

Ok, let's begin.

The rule states that:
Excessive bumping of threads is strictly prohibited. A maximum of 1 bump every 12 hours is tolerable.

It does not say:
Wait for 12 hours before bumping your thread.

These two statements are totally different.
Even if the seller bumps his thread five minutes after creating, that does not raise an alarm, as long as he doesn't follow it up with another bump within the given 12-hour period.

Meaning, that a seller is allowed a maximum of 1 bump every 12 hours.
It will be his decision when to use that 1 bump allocated for him, either he uses that bump 3 minutes after creating the thread or after 11 hours, it doesn't really matter.

Bumping after 5 minutes or bumping after 11 hours are the same. The same 1 bump. As long as there are no more bumps after that, it will remain as 1 bump, no matter how we look at it there is only 1 bump.

It will only become a violation if there are 2 or more bumps within 12 hours.
The illustrations below will help you visualize the different scenarios.