To delete a post just log in, then go to the message you want to delete. You will see an edit button in the top right corner of your message. Click on this and you will then see a list of choices below your message, the bottom of which is 'delete'. Once you click on this, you will then be asked again if you are sure you want to delete your message, click 'yes' and that's it... gone!
Just a thought, if you delete the one about The Singer's Singer set being for sale it will make the heading look a little puzzling, so you could always use the 'edit' button to add to your message that you have 'seen the light' and changed your mind, and that it is no longer for sale.
Anyway, it's entirely up to you which you choose to do.
I purchased both The Readers Digest set and Complete Heartbreakers on ebay. They come along rarely, but they do appear from time to time.
Good luck in your search.
Marian