As Vaishnavas we need a clear distinction what food is actually Krsna-Prasadam and what so called Prasadam we cannot accept at all. So let’s hear from His Divine Grace:
“TCC Madhya 22.87). A Vaiṣṇava must be very strict in this respect and should not at all cooperate with an avaiṣṇava. If an avaiṣṇava offers food in the name of mahā-prasādam, it should not be accepted . Such food cannot be prasādam because an avaiṣṇava cannot offer anything to the Lord. Sometimes preachers in the Kṛṣṇa consciousness movement have to accept food in a home where the householder is an avaiṣṇava; however, if this food is offered to the Deity, it can be taken. Ordinary food cooked by an avaiṣṇava should not be accepted by a Vaiṣṇava. Even if an avaiṣṇava cooks food without fault, he cannot offer it to Lord Viṣṇu, and it cannot be accepted as mahā-prasādam. According to Lord Kṛṣṇa in the Bhagavad-gītā (9.26):. When asked, “What is the behavior of a Vaiṣṇava?” Śrī Caitanya Mahāprabhu replied, “A Vaiṣṇava must avoid the company of an avaiṣṇava (asat).” The word asat refers to an avaiṣṇava, that is, one who is not a Vaiṣṇava. Asat-saṅga-tyāga,—ei vaiṣṇava-ācāra (
“When one eats food offered by a materialistic man, one’s mind becomes contaminated, and when the mind is contaminated, one is unable to think of Krishna properly.
Srila Bhaktisiddhanta Sarasvati Thakura suggests that people who are materialistically inclined and sahajiyas, or so-called Vaishnavas who take everything very casually, are both visayi materialists. Eating food offered by them causes contamination, and as a result of such contamination, even a serious devotee becomes like a materialistic man. There are six kinds of association — giving charity, accepting charity, accepting food, offering food, talking confidentially and inquiring confidentially. One should very carefully avoid associating with both the sahajiyas, who are sometimes known as Vaishnavas, and the non-Vaishnavas, or avaisnavas. Their association changes the transcendental devotional service of Lord Krishna into sense gratification, and when sense gratification enters the mind of a devotee, he is contaminated. The materialistic person who aspires after sense gratification cannot properly think of Krishna. (CC Antya 6.278)
Prabhupada says here that even if we are seriously engaged in devotional service we become materialistic by accepting food from Vaishnava posers or sahijyas.
Tamala Krsna: “It’s a great offense if you offer someone prasadam and they refuse. Prabhupada: Yes. That means I am not accepting you as intimate. And if he accepts, then you cannot deny his friendship.”
Srila Prabhupada Room Conversation, 07-10-76, New York