Tirmidhi

Explanation:
1:
There are various forms of deception in trade,
for example, concealing a defect in the merchandise,
mixing inferior and substandard goods with quality goods,
mixing something else into the merchandise in order to increase its weight, and so on.

2:
The meaning of "He is not from among us" is that he is not upon the way of the Muslims;
this action of his is contrary to the action of a Muslim.

Hadith Commentary: Benefits and Issues:
In this hadith, a form of deception has been described under which many specific instances fall:
➊ The upper part of the item is good, which is visible,
➋ and the lower part, which is not visible,
➌ is defective or inferior.
➍ In this way, adulteration and mixing,
➎ forgery,
➏ gilding (making something appear better than it is),
➐ and all those forms of buying and selling in which deception and fraud are found,
all come under the purview of this hadith.
And unfortunately, Muslims are committing these acts openly and without fear,
and everywhere the market of deception and fraud is thriving,
but Muslims do not realize how grave a crime this is, to the extent that its very conception cannot be attributed to a true and complete believer.

Benefits and Issues:
(1)
It is necessary for the scholar and the ruler to acquire direct awareness of the conditions of the people and to promptly warn them regarding their mistakes.

(2)
The deception in the grain was that some of the grain had become wet due to rain. The owner of the grain placed the dry grain on top, thus hiding the wet grain underneath. See: (Sahih Muslim, Al-Iman, Chapter: The Statement of the Prophet ﷺ "Whoever deceives us is not from us", Hadith: 101)

(3)
There are many forms of deception, all of which are forbidden, for example:
Trying to prove a lie as truth through eloquence, presenting falsehood in the guise of truth, not disclosing a defect in a transaction, and mixing inferior and worthless goods with good goods in order to receive the price of quality goods,
etc.

(4)
"The phrase 'not from us'" means that he is not upon the way of the believers.
In one narration, the words are (فَلَيْسَ مِنِّيْ) "he is not from me"; this also means that he is not upon my way, and such an act does not befit my follower. Therefore, every Muslim should avoid all kinds of deception.

(5)
Using unlawful means in examinations, such as cheating or copying, or an examiner giving a student more marks than he deserves, is also included in deception.
This results in the rightful individuals being deprived of their due.

Benefit:
In this hadith, it is clearly stated that people of knowledge should also go to the markets and fields, and wherever there is doubt, they should examine the goods for the purpose of investigation. If someone has kept counterfeit goods and is deceiving others, then he should be condemned, and people should be informed about the rulings of the Shariah.
Nowadays, almost everyone is deceiving, except those upon whom my Lord has mercy. Farmers also deceive in countless ways; when they bring goods to the market, they put the inferior goods inside and place the superior items on top. In fact, some worldly traders even mix corn into turmeric powder, and adulteration in milk is extremely common. May Allah Ta'ala grant guidance to the Muslim Ummah. Ameen.