Even if the account credentials work, the original owner will always have the original email address and proof of purchase. After you spend days downloading Forza Horizon 4 (roughly 80GB), the owner will simply click "Forgot Password," recover the account, and change the credentials. You are left with a partially downloaded game and zero access.
: These accounts are often stolen from other users and will eventually be reclaimed by the original owner or banned by Valve for violating terms of service. free steam account with forza horizon 4