Yes, if the buffer does not have mp, then it is not possible to purchase buff from them. When purchasing buffs it also requires you to have any item the the skill requires, ie spirit ore for prophecies. All buffs a character can obtain ingame, excluding super buffs such as hero, salvation types, mystic immunity etc; this is also including every skill enchant route up to +30.
PS: I did not cheap out on my own server, and i would not sell crap.