תנו רבנן: בראשונה כל מי שאבדה לו אבידה - היה נותן סימנין ונוטלה. משרבו הרמאין, התקינו שיהו אומרים לו: צא והבא עדים דלאו רמאי את, וטול.
The Rabbis taught: Originally, anyone who lost an item, would just offer the identifying marks and take it. When the liars multiplied, they instituted that they would say to him: go bring witnesses that you are not a liar, and take your item.
Apparently, claiming lost items was simply too easy for many people to pass up. Someone would announce that he had found a cellphone, and I guess it was easy enough for someone else to guess its identifying remarks that false claims for lost property became a common problem. So the rabbis, with this new institution, force us to assume that