M
MagpieInTraining
This site (and there are other diamond education sites like it that will give similar reviews) has reviewed many of the big names for diamond buying and Whiteflash & Brian Gavin rate the highest in terms of guaranteeing the best diamond quality. Tiffany is down the list.
https://www.prosumerdiamonds.com/
Yes, there are so many! I love beyond4cs.com for general diamond knowledge, and they also reviewed Tiffany/Cartier and ranked them pretty low on the list. James Allen is also highly recommended (along with Whiteflash and Brian Gavin).