One of the most likely pitfalls when buying heritage breed pullets is that the buyer ends up with males and not females.
The image above shows a pair of young Buff Cochins. They are about 6 weeks old. Only the male on the right shows quite a bit of comb growth. The wattles are often a better indicator of the gender, especially in breeds with rose, pea or walnut combs. The wattles are the red dangly bits under the beak. The pullet on the left has much smaller wattles than the male on the right. It is important that only chicks from the same breed at the same age are compared.