The Shulhan Aruch (Orah Haim 170:5) rules that a guest is obligated to do whatever the host tells him to. This is based on the Gemara (Pesahim 86b), which records the same teaching and adds the words “except for leave” in parenthesis. According to the Meiri, this emendation was added by a by what he terms a “clown” and may not be meant to be taken seriously. The Zohar, however, also records those additional words and therefore they require deeper analysis. If a host wishes for a guest to leave, how could the notion of ignoring the host’s wish be entertained ?
One explanation, offered by the Sfat Emet and the Vilna Gaon, is that the sentence should be understood as follows: “A guest must heed his host’s commands only in if said explicitly, except for ‘leave’”. In other words, even if the host does not tell his guest to leave outright, but merely hints at it, the guest should have enough common sense to understand and follow suit. The Hafetz Haim (Biur Halacha, O.H. 170:5), quoting the Bait Hadash and the Magen Avraham, explains that one should follow any directive one’s host, even if it is something that is beneath one’s dignity. One does not, however, have to heed a command to go to a certain place if that would lead one to do things that are beneath one’s honor, such as asking for directions or navigating an unfamiliar area.
The Mishna Berura (O.H. 170:16) explains that if one practices a certain stringency which is based on avoiding a possible prohibition, such as avoiding all vegetables so as not to accidentally ingest an insect, then one is not obligated to forego that custom if asked to do so by the host. If the stringency is simply an act of asceticism, such as fasting on a regular day, or a stringency beyond the letter of the law, then it should be relaxed if requested by the host. A practical application of this idea is that if one avoids foods with a certain Kosher certification because one considers it of a lesser standard, then one does not have to eat such foods even if asked by a host. If, on the other hand, the Kosher certification is considered Halachically acceptable and one avoids it for one’s own stringency, then if offered such food by a host, one should acquiesce.
Summary: One should heed any request or offer made by one’s host. If one has a stringency that is based on avoiding a certain prohibition, and not simply a stringency done in the name of self-discipline, one does not have to forego the stringency, even if asked by one’s host.