You're the artist.
The subject matter you choose is said to affect the marketability of your artwork.
While it's always wise to listen carefully to what a gallery director advises, you're the one making the art.
If you're serious enough to be taking an interview with a gallery director, you know the subject which most engages you.

• As the artist, you have the right to stick to your own choice in subject matter.
  The only requirement is that you do it in a style that is unique to you.
  And you must excel at doing it.
  The fact is: subject matter doesn't really matter.
  

Great careers are built on more than whether you paint landscape or interiors, portraits, nudes or still life.
Whichever subject impassioned you enough to stick at it, long enough to become a master, is the one that will make your career a success.
Mastery comes only with practice, long years of practice.
During that time, a style, as personal to you as your handwriting, will evolve.
It cannot be planned or forced or rushed.
It is the element that will identify your art, today and far into the future.
It's one of the factors that determine your art's appeal to buyers.

• People who buy art come in two varieties.
  

One is the person who relies on advice from others, such as investment brokers or interior decorators, rather than trusting to his or her own taste.
The other is the person who looks for high quality, in art as in any other object s/he buys to adorn the home.
To such a collector, the artist's craftsmanship is a vital consideration.
Even more important is the factor of meaning.
A true collector wants to invest in pictures that bring pleasure each time s/he sits down, alone, to look at them.
Pictures that evoke emotional responses, recall treasured memories or compel thoughts about the big issues of life and humanity: pictures with a story.
The first type of buyer will be content with any image large enough and colourful enough to 'make a statement' and complement the décor of a living room or office.
Today's art-world is stuffed with images of this kind.
Their chief value lies in the novelty of method by which they are constructed and the notoriety of their makers.

• True art collectors survive all the fads and fashions.
  Because they do, I predict the imminent return of what was, for centuries, the premier subject of master artists: the 'History Painting.
  '

Whatever your choice of subject, style or medium, your prime responsibility is to be true to your own art.
If you stick by this, you'll always give your audience the very best you can do, no matter what it costs you.