Deletion of threads?

Let's say a user contacts you to delete a thread for whatever reason - do you delete it upon their request or do you just lock it down?

Like yesterday, a game owner contacted me to delete a thread because his co-owner was trying to sell his game about a year ago and we found the thread, and I politely told him we don't delete threads, but I'll lock it down for you and add "Rumor" to the thread title.

He didn't say anything back, but really I'd hate to delete a thread upon request and personally always keep threads unless its spam.

How about you? Do you delete threads upon a user's request?