Delete them when you see them.
Just every ad you see online or in the newspaper.
This is an option.
You don't have to do anything, you don't have to even click on the notification to see what you 'could' send an offer on.
Watchers watch. Buyers buy.
Even without Best Offer being offered members can now send them. This is a change in policy, and not one I agree with.
You can reject, accept, counter-offer or ignore any Offer.