The Conference of Synagogue Rabbonim of Agudath Israel of America recently released a Kol Korei on the topic of ensuring that mezuzos are kosher.
Rav Yisroel Reisman Shlit”a goes in-depth in the video below to explain what to look out for and how a majority of Mezuzahs he has seen sold in Flatbush are Passul. “Klal Yisroel, we can do better” said R’ Reisman.
With all due respect to Rabbi Reisman Shlit”a, while he has some good points, such as many of us can do better and a Lamed should preferably have 2 tagin, (the right taller than the left), and Shatnez Getz tagin should preferably have ziyunim (little “balls”) on top and the Tzadis could be formed better, the fact is according to the vast majority, Lameds without tagin are kosher lechatchila, tagin without Ziyunim are choser hiddur and the Tzadis are kosher lechatchila.
He pointed out 2 spacing issues of which perhaps 1 was an issue. The Gimel with the bottoms being even is bedieved (and should’ve been corrected by whoever checked it) He commented that the Bedek Chaya tagin were a problem but in fact as long as there’s an oketz on the edge it’s mehudar. An indented tag with ziyun isn’t necessary. One, the other or both is fine. I commented about this in detail when this originally was publicized on another website.
He has excellent intentions but these matters should be handled by those with expertise in these matters.