“this was the custom in former times.” The custom that is described in Ruth 4:7 differs from the custom described in the Mosaic Law (Deut. 25:5-10), and also apparently differs from the custom as it was practiced at the time the Book of Ruth was written down, because the custom described here in Ruth 4 was the custom as it was practiced “in former times.”
“sandal.” The custom of giving up a sandal when land is bought, sold, or exchanged likely comes from the idea that the right to walk on the land belonged to the person who owned the land, and when a person no longer had a right to walk on the land then he gave up a sandal as tangible proof the land was not his. It also was a clear proof that the deal was done. If someone had your sandal, then everyone knew you agreed to the deal.