Homebot has no way of knowing if a buyer successful makes a purchase. If one of your buyers has purchased a new home, you'll want to add them into the homeowner side.

Buyers also have the option of adding themselves into your homeowner side: 

If a buyer becomes a homeowner or adds their home, they'll continue to receive Market Reports and the Digest. 

You can delete them from the buyers side so they no longer receive those emails.