Sri Caitanya Mahaprabhu is God Himself, but He was playing the part of a preacher. Every preacher should know that being allowed to touch a Vaisnava's feet and take dust may be good for the person who takes it, but it is not good for the person who allows it to be taken. As far as possible, this practice should ordinarily be avoided. Only initiated disciples should be allowed to take this advantage, not others. Those who are full of sinful activities should generally be avoided.