En anglais : A perfect transaction! You are very welcome!
En français : Vous venez de faire une très bonne affaire. Ndt: I don't have enough clue to understand what kind of transaction you are talking about. (The word "affaire" may change according to the meaning you want for "transaction") about the second sentence, do you want to tell her that she can come back whenever she wants? (Notre porte vous sera toujours ouverte) or do you want to tell her that you thank her for the transaction? (Je vous remercie) (Crédit : Sylang)