The householder should make a guest so welcome that he will never want to leave.
Even if the guest is an enemy, he should be treated so well that he forgets that his host is an enemy. See the example of Bhima and Jarasandha (Srimad-Bhagavatam 1.18.28 purport)
Even if a guest turns up uninvited, he must be offered a warm welcome and treated with all respect.
Even if the host is poor, he must at least offer a sitting place, a drink of water, and some sweet words. (see also Srimad-Bhagavatam 8.16.6 purport and Srimad-Bhagavatam 4.22.10 purport)