I've bought spuds from the store, from a local potato farm and have started growing my own. But have never had a problem with scab. But doing some reading I have found that the best way to store them, for prolonged periods, is to spread them out, keep in a dark area with temps around 45.
Here is some other info on scab. Hope it is of some help....there must be something that can be done about scab or potato farmers would eventually get it in their fields and be in big trouble.
Control: Plant resistant varieties whenever possible. We suggest using the russet-skinned varieties, since they have more resistance to the disease. Rotate root crops by planting in alternate locations to limit this disease. Potato scab is most prevalent in dry, alkaline soils. Decrease soil pH by adding elemental sulfur. The disease is controlled or greatly suppressed at soil pH levels of 5.2 or lower. Keeping soil moist during early tuber development may have a dramatic effect on common scab infection. Maintain proper soil moisture for about 2 weeks after the plants emerge from the soil. Avoid overwatering.