You can withdraw your offer at any stage before it is accepted.
This can be when the Buy Request is still Live or after the end date when the buyer is considering their offers.
To withdraw your offer you will need to Sign In, view the listing then select the Offers tab. From there select Withdraw My Offer.
However, if your offer has been accepted, you will not be able to withdraw your offer.
If this is the case and you are unable to proceed with the sale then your only option will be to Cancel the Transaction.