Shopping online is fine, but it really depends. I personally wouldn't do any shopping at a website if I don't know the company/website (for example, I'd be more likely to trust a company that has a physical store like... Forever 21, let's say, over a random person on Ebay), or doesn't have a whole lot of good reviews. If you have friends/family who have shopped on a certain site and haven't had any problems, that store is probably trustworthy.
Also, you can't try clothes on at an online store, so if your store has a size chart, by all means USE IT. That's actually super important, I've had friends who didn't refer to the size chart and bought clothes that were several sizes too small/big and didn't fit at all. sad
As for durability, most stores have a list of materials for the item you're looking at. If they don't, I'd be a little more cautious about buying from there.