@outofquagmire In this case you don't, Rabbi Mendel Kessin's Shiurim are available on Torah Anytime without needing checking. This is the shiur you are looking for https://torahanytime.com/lectures/310948
To answer your question (imho, I do not represent or work for Netfree), how are Netfree expected to know a random video online is a kosher shiur unless you send it for checking? The websites like Torah Anytime where all content is allowed without checking work with Netfree and have agreed only to upload content which fits the rules. You could suggest to the owner of torahthinking.org to do the same.