There’s a couple of ways to make bank. First is to start out rich enough to skip the loan and buy for cash. This is what companies like Blackrock do.

Another is to look out for things like tax auctions to get a big discount. Also you could be friends with a lender and get sweetheart rates on the mortgages.

Also, needless to say, it helps to never do any maintenance and to choose tenants that are unlikely to be able to fight back against you.