Be sure to check the tag for two-ply yarn (which means that two threads are twisted together). One-ply is too fragile and can be torn easily.
Avoid anything that is too fuzzy. Sure, it might feel incredible right now, but really fuzzy cashmere tends to sprout ugly pills very quickly. (But if fuzzy is your thing, pick up a sweater made with boucle fabric, they're amazing and SOOO fuzzy and soft.)
Avoid any cashmere that is too sheer. If you can see your hand through the fabric it's probably not going to be strong enough to hold up against the normal wear and tear of real life. (It would be nice to just sit around looking pretty all day, but most of us aren't that lucky lol...)
Always turn the item inside out to see how it's made. If it's knitted it will hold up better than if it had been sewn. Stitched seams tend to split open.
A high quality cashmere sweater should have a slight spring to it and hold it's shape well. Pull the sides apart and let them go. Does the sweater spring back into shape?
Sometimes lower grade cashmere is used in items that that are dyed darker. So if you're interested in a black sweater, make sure it's just as soft as it's more colorful counterparts.
Remember, high quality cashmere is usually somewhat expensive (even if it's on sale). So if you're buying a cashmere sweater make sure it's an investment that you won't regret later. No matter how much you love it, make sure you love how it looks on YOU. If it's just going to end up in the back of your closet, then what was the point of buying it? Keep your body shape in mind. Crewnecks and V-necks are flattering on just about everyone, so that is a good option if you want to play it safe. Turtlenecks tend to make torsos look longer and boatnecks can help balance larger hips. Colors like black, gray, and tan are the easiest to wear because their easy to match up with other items.
If you're looking to buy cashmere check out these beautiful sweaters...