A monk who has left home should never be overjoyed upon receiving offerings from others. Nor, however, should such offerings be refused.
The late Sojo (Eisai) said, “It goes against the precepts of the Buddha to rejoice upon receiving offerings. It also goes against the good will of the donor to be ungrateful.”
What we should bear in mind on this point is that the offerings are not to ourselves, but to the Three Treasures (buddha, dharma, and sangha). So, in acknowledging thanks, you should say, “The Three Treasures will surely accept your offerings.”