14. Chazal decreed an issur to make transactions [מקח וממכר] on Shabbos out of concern for writing (רמב''ם פכ''ג שבת הי''ב ). Accordingly, some forbid selling mitzvos on Shabbos and Yom Tov (הגר''א, בתוספת מעשה רב סע' ל''ד ).
15. However, most poskim are meikel (מ''ב סי' ש''ו סקל''ג ), and this is the minhag in most communities (ערוה''ש, שיירי כנסת הגדולה בהג' ב''י סי' ש''ו ). The reason is that it is for a mitzva matter, which is mutar [חפצי שמים ] (גמ' כתובות דף ה' ע''א, מהרי''ל הל' סוכה אות י', א''ר סי' ש''ו אות י''ט ); or it is allowed for the honor of the Torah (שו''ת מהרי''ק סי' ט'); or because it is for public benefit (מהרי''ל שם ); or there is no issur of transactions because the sale of mitzvos does not involve a tangible item (יש''ש ביצה פ''ה סי' ח', מ''ב שם, ערוה''ש שם ).
16. Changing the name of the currency. The minhag in some places is to only mention the sum, not the currency, at the time of the sale, e.g., “One hundred for Shlishi.” It is advisable for one who wants to buy a mitzva to ascertain which currency the aliyos are being sold in in that place. Otherwise, it can create shailos, e.g., if they are selling in dollars and he intended to bid in shekalim (עי' ס' שו''ת שמרו משפט ח''ב סי' ט''ז ).
17. Some use a different name for the currency, e.g., if the bid starts at ten, instead of saying, “Ten shekel, Shlishi,” they say, “Ten thousand, Shlishi” [the minhag in Ashkenaz is to say “tzen towzent” in Yiddish]. This change differentiates the sale so it doesn’t look like a real transaction (מו''ר הגרי''י בלויא בספר צדקה ומשפט פ''ד הע' י ').
