Thanks for the Business
I can almost guess, nothing, nada, goose egg.
Send a hand written note along with some flowers, chocolates or what ever turns your customer on. Absolutely DO NOT be cheap and send any denomination gift certificate from your place.
Your competitor is not writing a note because they didn’t get the business, this time. Don’t give them the opportunity to get it the next time.
Hand written cards, letters, notes, etc…say more than the words written on them. If shows your customers that you do appreciate them and their business.