Maaser Sheni, Chapter Four, Mishnah Twelve
1) One who says to his son, There is maaser sheni [produce] in this corner, but the son found [produce] in another corner, this may be considered hullin.
2) [If the father said] there was there a hundred [of maaser sheni] and the son found two hundred, the remainder is hullin.
3) [If the father said there were there] two hundred and the son found one hundred, it is all maaser sheni.
Section one: If a father tells his son that there is maaser sheni produce in one corner of the house and the son finds produce in another corner of the house, he can assume that the produce that he finds is not maaser sheni. We can assume someone took the maaser sheni produce and that which he finds is something else.
Section two: If his father tells him that there were 100 dinars worth of maaser sheni coins, and the son finds 200 dinars, then the extra is hullin. We do not assume that the father made a mistake and that all 200 dinars are really maaser sheni.
Section three: On the other hand, if his father tells him that there were 200 dinars of maaser sheni and he finds only 100 there, we have to assume that all 100 are maaser sheni.