I ordered several T-shirts from shirt.woot.com a few days ago. When they arrived, three of the shirts were huge, even though they were all supposed to be the same size. However, apparently they are switching between printing companies at the moment, so some of the shirts are in the old company's sizes, and some are in the new company's sizes. The website doesn't state that there is a difference in the sizing of the clothes. You have to look at the sizing chart for each t-shirt, even though the sizes are supposed to be universal.
When I first contacted them, they basically told me that they would not refund my money or do an exchange. I contacted them a second time, and was able to get them to make an exception. They are going to be sending me the shirts in the correct size.
If you choose to make purchases on woot.com, be very careful because they basically will not allow you to return products. It is only the rare exception that they will allow.