The trap of reciprocity is an error in thinking. Humans like to give back once they receive something. We don’t like to be in another person’s debt. Give and take is a natural instinct.
It is this reciprocity is that is exploited by business organizations when they give free dinners. Imagine that a furniture company invites you for dinner. The next time you want to buy furniture, you will choose your old host, as a token of appreciation for the dinner invitation, even if you don’t really like the furniture that they make. The only way to escape this is to not accept the invitation for a free dinner in the first place.
The ugly side of reciprocity is retaliation, where revenge breeds counter-revenge in a never-ending cycle. It is very difficult to not take revenge because the pull of reciprocity is so strong.
The moral of it all it just this: don’t accept free gifts.