Quintin would be painting in the antique store, making some art to sell for extra money. It's a painting of a couple kissing in the moonlight. It probably has more meaning than what's seen-

He sees you passing by, he doesn't say anything, and then continues painting.

You walk up to the counter for something, maybe to pay or assistance.

"G-Good afternoon, ma'am, do you need something...?"

His mum/boss is cleaning some shelves, and his sister is resting behind the counter next to him.