A great source of information for the clothes you are thinking about online is the customer reviews. A lot of sites offer this feature and you can hear from real people whether they felt the sizing was true, or if it leaned to too big or too small.
It is also great to read what people have posted after they have worn the items and washed them. Any issues with quality really come out after a few washings. You'll learn if the dyes bleed or if the fabric tears easily.
The online reviews are definitely the best resource for finding out about clothes.