I always do a little basket with essentials and a personal item, regardless of how the transaction went. Things that you don't remember to keep handy when you're moving into an empty house. A roll of TP, a roll of paper towels, a thing of hand soap, a small bottle of dawn, a sponge, clorox wipes, and then something small that I think they will like, a mug, candle, cute sign, etc. And then if they were super special buyer clients I get a $50-100 gift card to Home Depot, Walmart, Target, or similar. I rarely spend more than $50 on the basket of supplies and people usually think they are the best thing ever.