I think that all my exams have been marked correctly.
The thing is, a lot of people that whine about their exams being marked incorrectly have teachers that are too nice with the mark scheme. So, they get predicted As and A*s all year in mock exams, but when it comes to the real thing they don't answer things in the correct way and lose loads of marks.
For example, there are 3 ALevel Biology teachers at my school. My teacher is extremely strict with the mark scheme and won't give marks unless it fits the mark scheme perfectly / very very close. She's very specific. She is also an examiner for AQA. For example, when talking about why enzymes are specific, we have to say that 'an enzyme has a specifically shaped, 3D tertiary structured active site in which a substrate with a complementary shape to the enzyme's active site may form an enzyme-substrate complex with'. She has drilled very specific wording for all the modules on all topics into our heads all year. We got the results for AS yesterday and nobody in my class got lower than a C. However, the other 2 Biology teachers are very lenient with the mark scheme. For example, they think that there's no difference in saying 'less variety of habitats' and 'fewer habitats' and give the mark anyway: even though it should be 'less variety of habitats' when answering those Unit 2 questions on variation. So, funnily enough, quite a lot of people in those teachers' classes received U-D grades yesterday.
I mean, obviously the exam boards do make mistakes sometimes, but I'm getting tired of this culture of saying "EURGH IT'S THE EXAM BOARD'S FAULT THAT I GOT A BAD GRADE, NOT ME OR MY TEACHERS!". It seems people find it easier to blame an anonymous person than accept their mistakes and try again.
The best thing to do is request a photocopy of your exam paper with the examiner's marking, then you can work out where you have gone wrong - and if it seems they have marked it incorrectly, then get it remarked.