Now, ok, you can call me a corset snob if you want to. I mean, yes, I look at lots of really gorgeous corsets that I could never actually afford to own. And my own corsets that I make are by no means perfect, or even close to the highest quality corsets out there. But I've bought some really crappy corsets over the internet in my time, and I don't want others to make the same mistake.
So there are things to look for when looking at a photo of a corset. The biggest, number one indicator of real corset quality is wrinkles. The very best corsets have none. This is because the corsetiers who make these corsets have magical powers, I'm pretty sure. Check out this AMAZING corset by V Couture:
Smooth as anything. Also, probably the most beautiful corset I've ever seen.
Now, as I mentioned, you're probably only going to find this level of flawlessness in a couture corset handmade by a professional. But there are plenty of other levels of quality between this and complete crap mass-produced in China.
High quality corsets look hard. And I don't mean difficult to construct. I mean that the surface of the corset looks solid. This is usually due to a combination of high quality fabric(coutil) and lots of boning. This underbust is a great example of what I mean:
Compare the solidity and smoothness of this, with a mass-produced (but still somewhat decent quality) corset:
High quality corsets have a lot of boning. The job of boning in a corset is to hold the fabric taut, preventing it from getting crushed or crumpled or wrinkled. Steel boning is what you're looking for, but you're also looking for the quantity and placement of the boning. All corsets should be boned at every seam. Some are double-boned, meaning there is a bone on both sides of each seam. Often there are bones in between the seams, too, unless the panels are very small. What I see a lot of in low-quality corsets are large panels with no boning within them. It gets to the point where I'm thinking of this garment as a lightly boned top rather than a corset. Here's an example of what I mean:
Now, don't get me wrong. I like the style of this corset. It's unique. I pinned it for a reason. But looking closely at it, there are probable four panels for each side of the corset, eight in all. That's a really low number for corset panels. It means it's difficult to get much actual shaping with only four panels. This isn't going to cinch your waist. Plus, the only boning is on the seams. There are only a few seams, so very few bones. You can see how loosely draped the fabric is, free to wrinkle all it wants. I would not consider this a "real" or "serious" corset.
Finally, a quality corset is going to cost a few bucks. Now that can range from $60-600, depending on the corset and who made it. But if you find a deal too good to be true, like a $10 corset on ebay, it IS too good to be true. For more about the differences between a designer corset and a cheap Chinese knockoff, this is a GREAT article and video from Fairy Gothmother.
So I hope some of this information is helpful when you're trying to judge the quality of a corset. If you want some more corset eye-candy, take a gander at my Corsetry board on Pinterest.