With the progress of internet, e-commerce websites are increasing and people are preferring to buy stuff online to save some time or just because of some laziness . But that's okay because not everything is available in some stores. You'll probably find much variety online and I'm sure you won't have a problem with finding your size.
But be careful and stay away from spam or fraud websites because in this way, you can be conned and you won't get anything in return for the money you'd pay. Try to buy stuff from genuine and famously known websites.
Even though online shopping seems perfect but there are few stuff that you won't be satisfied after buying, like the quality or the size you expected. But also keep in mind that not all e-commerce websites do the same.
1) Gym Shoes
Now if you're buying sneakers purely for fashion purposes, by all means do so online. But especially if you're a runner, consider visiting a store and getting input from a pro. Shoes worn during workouts can affect bone and joint health, and getting the right fit can be essential to avoiding injury. Buy in person whenever possible.
This entire category of clothing is likely to need some tailoring, But you'll get closer to your best possible fit by shopping for suiting in person. Blazers are especially tough to get right since shoulders, sleeves, waist, and length all need to be in perfect balance. Department stores are always a good resource, but J.Crew and Banana Republic should have some options in-store, too.
3) Button-front Shirts
4) Anything over-sized
On the opposite end of the fit spectrum from button-fronts, we have swing coats, chunky knit sweaters, billowing tunics, and exaggerated wide-leg pants. You really never know how an oversized garment will interact with your curves and proportions until you get it onto your body, so eyeballing fit online often fails. However if it's something like a cozy sweater that's meant to look a little bulky, and/or you're not overly concerned about adding volume to your silhouette, online is just fine.
5) Kitchen Utensils
I don't completely disagree for buying kitchen utensils online but at times, you won't get the quality as promised and maybe the size of the utensils won't appear the same as you saw in the commercial or advertisement.
Parts of this article are inspired and taken from :
Shoppingtips.about.com (By Sally McGraw)