In my experience, it is exceptionally difficult. Perhaps one of the most difficult niches. I have 5 domains in this field, one of them with amazing rankings. Traffic is low and conversions suck. Art needs to be seen in the flesh, is my take on it, except perhaps if you're buying a standard poster print of some well known piece. Otherwise, I failed dismally and wasted a LOT of money. Much more effective is doing gift fairs etc and shifting it in person...