Shulchan Aruch of Rabbi Shneur Zalman of Liadi, Volume 12: Choshen Mishpat

On the contrary, when a friend visits and is not invited for a meal, this embarrasses him, as it implies that the host is not desirous of his company

One should not send a friend a barrel of wine with a layer of oil floating on top of it, for the recipient will think that the entire barrel contains oil.84 He [might] then invite guests to partake of it, confident that he has an abundance of oil for their needs and then he will suffer embarrassment.

Similarly, one should not send [a friend] a large gift, knowing that he will not accept it,78

If, however, one is merely in doubt, one may press for repayment.

Thus [his friend] will be grateful to him without cause.

necessary to measure generously, [giving the purchaser slightly] more than the measure, as it is written:36 “You shall have a perfect and just measure.” What is meant by a “just measure?” That you should justify [the measure] from your own and give it [to the customer].

modern day application of this principle, painting a used car to make it more attractive. On one hand, the year and model of the car is always stated, so there is no fundamental deception involved. Moreover, most serious purchasers will have a car inspected and a mechanic will be able to determine if there is any severe damage. Nevertheless, when p

the barrel was already open, but the host made it appear that he is now opening it in honor of his guest.

Likkutei Sichos, Vol. 27, pp. 151-152, the Rebbe explains why concern is shown for discrepancies in measures that would usually be considered as insignificant. Measuring implies that a person desires that the transaction be exact and — by using an inaccurate measure — the person uses that very activity to deceive his colleague.