FM have a database which stores pretty much all the "ranked" BRR players. Think of it like the CheaterBoard in Asphalt 8 but with no ban trigger. The devs then will check the entire database (which in my books, should display all the sensitive information like currencies and progress) and will then ban the "obvious" cases with 5-digit gold and above. I myself am an engineer / data analyst and I've worked with some huge Big data (Databases with millions of entries and types) to tell how easy it is for FM to at least detect the obvious cheat cases. As for the top ranked players, I've seen 2 of the top 3 players which are infinite Nitro users, but they use it in a very smart way to never break imossible track times (which I believe is a ban trigger as well). They also do not use hacks like "unlock all cars" since that'll make the cars like the Venom GT and the One:1 tunable, or at least, they specifically unlock those cars with not enough stars to be detected as hackers. The report tool is, according to the kids complaining in Reddit, useless as of now, but FM still sometimes rely on it to perform some quick bans on obvious accounts.
It's all about playing safe and smart, never having excess gold (9999 max in my books) when ranked in BRR, and preferably no other currencies hacked as well (like Tuning points since it costs real money and/or some serious TT farming), and also NEVER using a tuned Venom/One:1.