While the 1918-D Lincoln cent is common in circulated, it is decidedly rare in the Red Gem grades, with only a handful of pieces known in MS66RD or better. The 1918-D is notorious for some soft strikes, caused by worn dies being used beyond their normal operating lifespan. So, be choosy on the purchase and avoid examples that exhibit weak strikes or other issues. As always, pieces with decent color and strong strike will provide more satisfaction to the eye and possibly yield a better return on investment when the time comes to sell.