In essence: selling your A-Level certificates does not confer upon the buyer your A-Level results.

But they know about horses

I don't know. Play it how you want!

See if there are any other groups? Like if the group you've spotted would make two other groups unworkable, then maybe the other groups are right and yours is wrong? I guess play how you want, but you're going to need to think ahead a bit if you want the perfect score

Red herrings are a perfectly normal feature of puzzle design, and if you're spotting one group and then immediately clicking on it they you're doing it wrong (except not really because you're allowed multiple guesses).

The fact that the word 'policeman' is used here says a lot about what Americans think policing means.