I have been in sales my whole life.
Even when I was baby, I was selling myself by being irresistible and needy! As I grew up, I learned to use my brains and charm to win others to my way of thinking, to "buy in" to what I wanted. If one goes into sales, as I have, we continue to sell ourselves because if we don't, no one will buy our product from us.
BUT the sale is NEVER COMPLETE until the THANK YOU is expressed. As a baby, that was done with a smile and a happy burp after we were fed. As a Sales Professional, that is done with a Thank You at the close of a sale or a deal. If we are smart, we also thank anyone who sent us a referral, connected us with another in our business sphere, remembered our birthday, acknowledged an achievement.
When you say "I appreciate..." , do it with a written note, mailed to the recipient, an art that is all but forgotten. I use an online system that allows me to do this in my own writing over my own signature. Feel free to ask me how.
It doesn't matter how, it only matters that you say "Thank You" every at opportunity.