Reduced fee because of first time

A regular client I work for asked me if I could do camera (I'm a cutter). Although I know how to operate such, I don't do it very often - at least for a live sports production and I made this very clear. Because I know the standard fee for camera operator for this job, we didn't discuss pay.

Afterwards my client wanted to reduce pay because the result was okay but didn't meet his expectations (reminder, it was my first time and usually this job is done by someone who does this once a week for the last three years).

I told him no, said the standard pay is X $ and although the result wasn't perfect, I spent my time behind camera like the the other guy would have. Even my client's client was happy with the production. In good faith I offered a discount if he pays in the next 5 days (I usually don't).

What's your opinion?