Some of the greatest Rishonim would refrain from eating a new fruit or buying a new garment during the Three Weeks, in order to avoid reciting She-heĥeyanu. They reasoned: How can we say, “Blessed are You, Lord…Who has given us life, sustained us, and brought us to this time” during a period of such misfortune? (Sefer Ĥasidim §840). Even though some of the greatest poskim felt that one does not need to follow this stricture (Taz, Vilna Gaon), over time it became customary to be stringent and avoid reciting She-heĥeyanu during the Three Weeks. Therefore, we take care not to eat any new fruit or buy any new garment that would require one to recite She-heĥeyanu.
However, until the end of Tamuz one may purchase items that would not require one to recite She-heĥeyanu. For example, one may buy socks or undershirts, because these items of clothing are not significant enough to warrant the recitation of She-heĥeyanu. One may also purchase shoes if it is not his custom to recite She-heĥeyanu over them (SA and Rema 223:6; also see Peninei Halakha: Berakhot ch. 17 n. 4). Similarly, a couple may buy a piece of furniture, because, as partners in the purchase, they recite the berakha of Ha-tov Ve-hametiv rather than She-heĥeyanu. An individual, on the other hand, must refrain from buying furniture to avoid reciting She-heĥeyanu (SA 223:5; Peninei Halakha: Berakhot 17:3).
Until the end of Tamuz, one may also buy a fancy garment that requires alterations, to be worn after Tisha Be-Av. Since it cannot be worn at the time when it is purchased, one does not recite She-heĥeyanu at that time (MB 223:17). Furthermore, according to those who customarily recite She-heĥeyanu only when they first wear the clothing (which is the prevalent custom), one may buy a new garment during the Three Weeks, on the condition that he wears it and recites the berakha after Tisha Be-Av. Once Av begins, we minimize our business dealings, and so it is proper to avoid such a purchase even if one will not recite She-heĥeyanu at the time of purchase (see below, section 18).