When buying clothing to sell on eBay, be sure you have the right sizes in your business inventory. The average American woman's dress size is 14 (the beginning of plus-size clothing), not an 8; the average American man is a 40 regular. When buying apparel for your eBay business in lots for resale, ignore the standard "1 small, 3 medium, and 2 large" lot, and instead buy 1 small, 2 medium, 1 large, and 1 extra-large.
When selling apparel, be sure to add measurements. A site like Size.ly can help you tailor the measurements to your garment.