I have (thankfully) not sent an email to the wrong person, but a funny thing happened to me last year:

We were in the porcess of buying some limited edition fountain pens (they are a great investment). The broker sent us the banking details for us to transfer our payment, but instead of attaching OUR invoice, he attached HIS COST PRICES!! Of course then mwe went back to him and asked for more discount He was VERY upset!!!