Answer:
Xenia or the custom of showing hospitality to guests is one important custom in Greek culture that plays an important role in "The Odyssey".
One violator of this custom is Polyphemus or even the suitors and an example of the observance of this custom is Nestor.
Explanation:
One of the most important customs in Greek culture is the concept of showing hospitality to everyone, regardless of who the person may be or may come from. This concept which is termed "xenia" is extended even to strangers. In this, guests are welcomed in any place, given safe lodging and food and even let go laden with gifts from the host. This concepts played an important role in the culture of the Greeks in Homer's "The Odyssey".
One person who violated this custom are the suitors in the palace of Odysseus' home. They ate and drank to their fill for so many days, yet do nothing in return. Rather, they oppressed and made life for their host and even tormented them.
An excellent example of the observance of this custom is Nestor, "knight of Gerene". He had provided food, transportation and gifts for Telemachus' trip, along with sending his own son Pisistratus to accompany him in his search for Odysseus. (Book III)
Another violator can be Polyphemus who ate his guests when Odysseus and his men came upon his cave. But then again, we can also say Odysseus and his men are also violators for stealing things from their host.
