PriceYak can automatically increase your item quantity after sales. By default, PriceYak will keep your item quantities at a minimum of 2.
This is the optimal default for most sellers who are listing at or near their current eBay selling limits.
A quantity floor of 1 might be preferable for aggressive sellers who would like to list more items given there selling limits. And a quantity floor of 5 might be preferable with for sellers with high or no-limits eBay accounts.
You can change this item quantity setting on your Store Settings page. Find the Repricing Settings column at the left and scroll down to the "Quantity in Stock" field. You can change this at any time.