When buying tourmalines, it is important to consider color, cut, clarity, and carat weight. Tourmalines come in a wide variety of colors, from traditional pink and green to rarer colors such as red and yellow. Look for a well-cut stone that displays the tourmaline's unique color and fire. Clarity is also important, as eye-clean stones are more valuable. Lastly, carat weight should also be considered, as larger stones are more valuable, but keep in mind that a higher quality smaller stone is worth more than a lower quality larger stone. Additionally, consider the origin and the treatment of the stone, as untreated tourmalines are considered more valuable than treated ones.