Are there any well known/well regarded websites to buy cosplay from? I feel like in the past when I've looked into it the sites have looked a little sketchy to me. I'm scared of ordering something that looks great online and is a huge disappointment irl.
I've actually dressed up for one convention in the past. Some of my friends go to Anime Boston every year and I decided to go with them one year. They always go dressed like soldiers from various wars - so not exactly cosplay. The year I went they were dressed as American soldiers from the Vietnam War. I got some sort of like sexy female soldier costume and a shake and go wig and went in drag with crazy thigh high heels on. Everyone thought it was hilarious that I was there with these boys who were dressed in serious costumes and it kinda pissed off one of my friends because everyone wanted to take pictures with me.
I would say Etsy isn't so bad, although that site is being bombarded with cheaply made, run-of-the-mill items now. I've had a lot of success buying nice quality things on there, though not cosplay related. I would recommend starting a conversation with the shop owner first, just to ask some questions about the product, and try to determine if they seem like someone worth buying from.
You can also look around DeviantArt. It's not exactly a shop, but some people sell their creations on there. Unfortunately once in a while you'll find something really nice from someone not selling, so you can only admire their work. In those cases, I would say ask them if they can recommend someone who creates similarly. At very least they won't recommend anyone, at best you'll find a similar item from someone who does want to sell.