They'll ask their question (where are the download details, why am I getting this error mesage etc.), then sign it off with 'I hope this isn't a scam'.
Think about it logically for a minute...what is the point????
A scammer wouldn't care if they wrote it. It wouldn't make them change their mind or method of operating their scam website & suddenly send through their access details or help them with their download problem.
If the person running the site is honest, they will get a reply regardless of whether they write 'I hope this isn't a scam'...& by writing that (effectively suggesting that they think you might be a scammer) they may well annoy (slightly) the perfectly honest person who's running the site.
So, in summary, that comment won't affect a genuine scammer & may come across as a bit offensive to an honest person...so why say it?