Asking for Basic Provisions on Shabbos

It says in Shulchan Aruch OC Siman 323 Sif 4 that one may go to a store owner and ask for a number of beitzim on Shabbos as long as the price is not mentioned. Why, even without mentioning the price is there not a gezera that one might come to write?

Answer:

For basic provisions that are required for Shabbos, Chazal did not make a decree, provided that the price is not mentioned.