My advice is if you are going to shop at a thrift shop, do 2 things: visit a good one and check your merchandise thoroughly. One of my local thrift shops is always kept very clean, no stuff on the floors, and the clothing is sorted by type, size and color. This makes searching easier and faster. If you check your merchandise well and make sure there are no holes, stains or excessive signs of wear, you can leave with a quality item at a low price.
This doesn't just go for clothing, but also for decorative items, items used for crafts, kitchenware and furnishings.