How do I edit or delete an offer once it has been made?

There are two possible scenarios here:

A) The Lister has not accepted the offer

If the Receiver decides, before the Lister accepts an offer, that they don't wish to continue with their offer, they can select 'Cancel Offer' in 'My Activities'

B) The Lister has accepted the offer

If the Receiver or Lister decide, after the Lister has accepted an offer, that they do not wish to progress with a trade, they can email one another to mutually agree to cancel and then, the Receiver can select the ‘the goods/services/tasks' were not provided’ to automatically void the transaction or they can just leave it and two weeks after the agreed trade date the offer will automatically cancel (these actions will not negatively impact the Listers' feedback ratings).