Did the manager realise that when e venue fills up, the band will sound a lot quieter?
If the person can make or break gigs for you, work with them, if they can't, then do as you please.
I played a beer festival several years ago where we were the only band (well, there was 2 bands, but I was the bassist in both).
A woman & her 2 kids sat right at the front, about 8 foot from the front of my rig.
First song & she said "you're way too loud, can you turn it down". I explained that she was sat right in front of the speakers & moving to a different table would be much quieter. She wasn't happy, so I turned down a little.
Another song in & the organisers came over and asked us to turn up, a lot.
She wasn't happy & complained to the organisers who then gave her a nice seat at the back.
At the end of the first break, she came over & complimented the band.