Yeah, one thing to be aware of in American schools, practically every grade counts. Every test/exam, project, book report, pop-quiz, spelling/vocab test, homework assignment etc. All of it averages together throughout the year. It'd be pretty easy to boost the odd mark here and there, especially on stuff done earlier in the year where the teacher wouldn't have a hope of remembering what they put. It's not like here where you've pretty much got two grades: exams and coursework project. Teachers here would be more likely to remember those, maybe.
They got greedy with selling on the mark schemes, that was their downfall. They didn't prevent traceability of the mark schemes back to them, and they didn't have a back up story to explain how they came across them. They got caught, then did a full ****ing confession. Morons.