There's absolutely no risk of ban for unlocking every car in the game? Sounds like that's almost a surefire way to get banned, they will notice eventually because they are losing money for those cars that require purchases, especially if you are unlocking unreleased cars.
If I recall correctly the communities of the free FH5 menus/tables have specifically advised against unlocking unreleased cars for this exact reason. If it's not bannable now it is extremely likely they will catch on. It's not hard to add a server-sided check to see if you actually own the expansion that the car you're driving is in.