We always give the Seller a gift after the closing of a property that we listed.  It depends on the price of the house and what the Seller likes.  I have given gift cards, flowers, fruit baskets, potted plants, etc.  The idea is to thank the Seller for trusting you in the process of listing their property and closing the deal.  In some of the deals I have given the Buyers a present too.

Sincerely