THANK YOU FOR DROPPING IN
I would just like to thank you for dropping in [DATE, ex. on Tuesday]. It is always a pleasure to see you. [FOLLOW UP ON CONVERSATION, ex. I have taken a look at your order, and have determined that a slight error on the part of our suppliers is to blame. We will be shipping the compressors to you today and you should receive it by the end of this week.]
I look forward to seeing you again.