Guest Posting By Rabbi Shmuel Rosenberg - Minhag Yisroel Torah He
I heard the following story from Rav Gavriel Tzinner, shlita, author of Neta Gavriel, an encyclopedic work on minhagim, and a respected Rov in Borough Park. Since I'm a sofer, he mentioned this to me:
Once a group of non-Jews came to the leaders of a certain Jewish community to sell them a Sefer Torah. However, the Jews didn't know if it was written by a Jew or a gentile (in which case it would not be valid). So they asked the illustrious Rav Akiva Aiger. He simply said, "Minhag Yisroel Torah He (the custom of Israel has the status of law)."
They didn't understand him, so he explained what he meant: the "Minhag Yisroel" is to leave a few lines at the end of the Torah for the sium (ceremony of finishing the writing, followed by a celebration) in which the letters are hollow -- just outlined. The people in the community are given the honor of filling them in, and of course, these last words usually gets slightly messed up, because most people don't know how to use the kulmos (quill). (When I write a Sefer Torah, I go over it after the siyum to fix it up and make it as nice as possible.) So Rav Akiva Eiger told the group, "If you see that they followed the minhag Yisroel on this Torah and the writing at the end is messed up a bit, then 'Torah He' -- then it's a kosher Torah. But if it looks too perfect at the end, then you know it was written by a non-Jew and should not be purchased."
So we see from this how important a Jewish custom can be!