This letter praises a company for its good treatment of a friend or relative whom you referred to them.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
Not long ago, I sent <person you referred> to you for <referred person's need>. I just wanted to write to say thanks for treating <him/her/them> so well.
I appreciate the care and service you've given <person you referred>, and I'll be happy to refer more customers to you in the future. Thank you.
encl: <List of enclosed items goes here>