I love shopping on Sammydress so much that it's on my bookmark bar. I've loved everything I've purchased, and haven't had a problem with quality--I mean, you're typically paying less than $10 per item, and the items still tend to be better quality and less expensive than at a bargain mall store.
I placed an order on a Sunday, and promptly received a confirmation email. The next day the first part of my order shipped (everything that clearly said "shipped within 3 business days" right on the items' pages), and I received the order on Friday. The other things that clearly said "shipped within 5-10 business days" were, in fact, shipped within 5-10 business days. Seriously, if you just READ everything thoroughly before you make a purchase, you'll probably have a great experience.
Same goes for sizing. I'm a US small, but buy medium or large on Sammydress. Asian sizing is different--just read and do the math, and you'll do fine.
In summary: Don't be scared away by those who did not read thoroughly before placing an order. The site is very clear about shipping and sizing if you pay attention. Read first and you'll enjoy the most affordable and fabulous deals you can find.