Reciprocity is a cultural concept, not as prevalent in our times, where if one is given something, something is expected to be given in return. This is not about greed or forcing someone to give you something, but in times past, the rules of social niceties simply dictated that people shared often and happily with one another, and everyone was compelled to do this - there was no opting out of hospitality! You can still see this concept reflected today in some holiday gift-giving attitudes; it can still give you an apprehensive feeling if someone purchased you a gift, and you had not gotten one for that person.
A relationship of reciprocity is the most common way to relate to spirits in ADF Druidry. Whether they are your Ancestors, Nature Spirits or the Deities themselves, it is helpful to establish these kinds of relationships. When a practitioner makes a sacrifice or pours a libation to the spirits, this is a gift that the spirits will return in kind. Now, some who come from a more mystical background see this as demeaning, as if reciprocity is simply drawing up a contract, and disrespectfully expecting the spirits to give up their gifts like a cosmic vending machine. This is not so at all! The Indo-European spirits with which most ADF Druids or Heathens honor have a cultural basis in this type of relationship; it is not seen by them as disrespectful, but instead is an honoring of an age-old way of relating with the spirits. Others who come from a more magical background may also see the relationship of reciprocity as different than it really is; it is easy to equate it with magical workings where one invokes a spirit and expects that spirit to follow their will. But this is also not a good comparison. The relationship of reciprocity is not one of power or command, any more than a gift given in good faith is a command that another one be given. It is a cultural relationship, in which the door is wide open for a spirit to say 'no' to the worshiper's request, and to grant something more to the spirit's liking instead (this is why I find it prudent to stay away from trickster deities in my practice)!