May a wife let guests into the house when her husband is away?

A wife does not admit anyone her husband dislikes into the home without his permission; usual visitors such as close family and female friends are generally covered by his general permission.
The Prophet ﷺ said that a wife should not let anyone into her husband's house except with his permission (Sahih al-Bukhari 5195). Scholars explain that this permission can be general, according to custom: the wife's parents, siblings and known female friends do not need permission each time. What should be avoided is admitting non-mahram men while the wife is alone, because of the prohibition on being alone together (Sahih al-Bukhari 5233). Repairmen or delivery staff are better dealt with at the door, or when someone else is at home. The same principle applies to the husband: respecting his wife's feelings about whom he brings home. See Modesty & boundaries.