I will use my sizing as a benchmark.
Size: 5'1'', 102 lbs.
1. The "one size" fits all - are more over-sized than anything else. I bought a hunter green sweater and aside from it being huge; once you roll the sleeves and throw on a turtleneck or tee under to prevent the itchiness, its actually a great piece to wear under tights or skinny jeans. For $17.99 it wasn't that bad.
2. The sizing - perfect for me. I think the sizing is based on small Asian models which works to my benefit. I would say a "small" is more equivalent to an "x-small" and so forth. I bought a navy sweater with pink flowers (can be seen on my earlier post) from sheinside.com and it actually fit perfectly for my frame. Note to remember: if you have a bust - I would try to size up (or the one size fits all) - sites are not very bust friendly all the time.
3. I know a lot of people are skeptical with putting their credit card information on these sites. I have been fine so far, but if you feel uncomfortable, type in what you're looking for on Amazon. A lot of third party vendors actually carry the same stuff. That way, at least you have Amazon's backing if shipments get lost.
4. Be patient. It takes forever for these items to come (because they are coming from China!). Don't freak out when you don't get what you ordered in a week or two. It can take upwards to three - four weeks. Just let it be and it will come. If they don't, I have heard horror customer service stories, so be cautious. Also, I have heard they wont pay the shipping fee (which is probably astronomical since it's going back to China), so do a benefit/cost analysis. It's a gamble.
5. Great Blanket Scarves - Amazon and these sites carry all the blanket scarfs that boutiques and Zara sell for like $25-35. Instead you're paying $10-$15. I have about 30 of them, and the quality is just the same as the others. So soft and cheap! I would highly recommend getting these from Amazon. I have never had a problem from anything I got here.