Maaser Sheni, Chapter Four, Mishnah Five
This mishnah teaches a way for a person to redeem his maaser sheni without adding a fifth, even if he doesnt have any coins in his hand. This is another form of deceptiona legal means by which to get around paying the added fifth.
One who was standing at the threshing-floor and didnt have any coins may say to his friend: Behold, this produce is given to you as a gift, and then he may say again, Behold, let this produce be exchanged for money which I have in the house.
If this person had coins in his possession he could simply give the coins and the produce to his friend and have his friend redeem them for him. However, since he doesnt, he must make a slight modification. First he officially gives the produce to his fellow, and now it legally belongs to the other, even if he intends to give it back.
Now that the maaser sheni produce belongs to his friend, the original owner can redeem it by using coins that he has in his house, without adding the extra fifth. Had he simply redeemed them without first giving them to his friend, he would have had to add the extra fifth.