Business Or Pleasure?

It is generally assumed that commerce is forbidden on Shabbos and yom tov due to a rabbinic decree. If people would engage in regular buying and selling on yom tov, they might mistakenly write down details of their transaction. Writing is definitely a biblically prohibited labor on Shabbos and yom tov. Rebbe Akiva Eiger, based on a Rashi in Beitzah (36a), suggests that engaging in commerce on Shabbos or yom tov may actually be biblically forbidden.
There are, however, permissible ways to buy things on yom tov on a small scale without the use of money. Among the requirements for the leniency is that there must be a significant change from the way the sale is normally transacted on an ordinary weekday. An example of such a change is that the price should not be discussed. (See Shulchan Aruch O.C. 323.)
When one gives a present, by definition there is never a discussion of the price. (The recipient begging to know how much you paid doesn’t count!) Hence, not mentioning the price of a present would not differentiate it from a weekday transaction. The Mishnah Berurah (306:33) therefore writes that giving presents on Shabbos is not permitted.