It is customary in all synagogues that a "Gabbai," or "Mesader," stands near the Torah during the Torah reading together with the Ba'al Keri'a (reader) and the Oleh (person called to the Torah), and is responsible for calling congregants to recite the Berachot over the Torah.
The Mishna Berura (commentary to the Shulchan Aruch by Rabbi Yisrael Kagan, the "Chafetz Chayim," Lithuania, 1839-1933) cites two possible reasons for this practice (141, s"k 16). Firstly, our reading of the Torah corresponds to Matan Torah, the giving of the Torah at Mount Sinai, and should therefore resemble that momentous event. The Mesader who calls people to the Torah corresponds to the Almighty, as it were, who summoned Benei Yisrael to the mountain to receive the Torah. The Ba'al Keri'a reads the Torah for the Oleh just as Moshe Rabbenu taught the Torah to Benei Yisrael. Thus, the three men who stand by the Torah scroll during the reading serve to commemorate our initial receiving of the Torah at Mount Sinai.
The Mishna Berura then cites a second explanation from Masechet Sofrim, namely, that the three men at the Torah correspond to our nation's three patriarchs – Avraham, Yitzchak and Yaakov.
In this context, the Mishna Berura cites a passage from the Sha'arei Efrayim (a compendium of the laws of Torah reading by Rabbi Efrayim Zalman Margaluyot, Russia, 1760-1828) regarding controversies and misunderstandings that occasionally arise in the synagogue with respect to the distribution of Aliyot. At times a person is called to the Torah and feels insulted for having been chosen for the given Aliya, rather than for a more distinguished honor. It is all too easy in such cases for the individual to accuse the Mesader of deliberately attempting to insult him. In order to avoid such situations, the Mishna Berura advises, congregations should choose as a Mesader a well-respected and well-liked individual who has achieved a reputation of integrity. Such a person is not likely to be suspected of distributing the Aliyot on the basis of personal vendettas and agendas.
The Mishna Berura adds that if it so happens that the Mesader does insult a congregant, the congregation should judge him favorably and assume that this was done inadvertently, and not maliciously. And the Mesader, for his part, must ignore any insults or scorn directed to him by the congregation. The Mishna Berura rules that if in response to a congregant's insults the Mesader leaves the Torah scroll and returns to his seat, he should be punished for dishonoring the Torah scroll. The fact that he was humiliated does not authorize him to infringe upon the honor of the Torah scroll.
Summary: The Mesader, who calls people for Aliyot to the Torah during the Torah reading, should be a well-liked person known for his integrity, and must ignore any insulting comments made by disgruntled congregants. And if it appears that he infringed on somebody's honor by calling him for the wrong Aliya and the like, the congregation should assume that he made an honest mistake, and did not intentionally insult the given congregant. Furthermore, 3 people should stand at the Teba during the reading.
