A high-quality watercolor brush must possess three attributes: Point, Snap, and Flow Control. The brush should come to a crisp, fine point that doesn't split during use. 'Snap' refers to the bristles returning to their original shape immediately after a stroke. For Flow Control, the belly of the brush must have a high absorbency rate, allowing for long, continuous washes without frequent reloading. Requesting a video demonstration of a 'spring-back' test and a water-loading capacity test from the supplier is highly recommended.