I've been buying silk scarves for 30 years. During this time, I've noticed there is an incredible range of quality that exists for what you can buy. "You get what you pay for.", is something you need to keep in mind.
Here are the five aspects that I recommend you evaluate when you are contemplating a purchase:
Weight Dimensions Design Color Finish
Weight- The heavier the weight, the more it costs to make. Silk is weighed in mommes. Retail labeling does not generally state what this is for a given scarf. But you can tell what it is to some degree just by holding it. If it has a very sheer gossamer look and feel, it's going to be very light, potentially 4 or 6 mommes. If it is fairly substantial with strong coloring that holds up to light, it is probably 10 to 12 mommes. Much heavier than that, you are getting into weights that are better suited for drapery and upholstery. My favorite weight for silk scarves is 12 mommes. It's a perfect weight, not too light or heavy.
Dimensions- Each of the possible shapes of scarves out there comes in different dimensions. The larger the dimension, the more it costs to make. In general, the larger the better. My favorite dimensions in a square are 35" x 35". And for an oblong scarf, 16" x 60". These sizes work the best with the standard ties you can make.
Design- We are getting into more subjective ground to a certain extent. But, if you begin to spend any time studying patterns, you can tell when they are thrown together or not. Yes, it's true, fads can include thrown together looks. A poor design, though, looks tacky, plain and simple.
Beautiful silk scarves have beautiful, well thought out designs. They are attractive to look at. You enjoy gazing at them. They always enhance what they are being worn with.
Color- This is fairly subjective too. I will say though, understanding good colors and how to work with colors seems to come naturally to some and not to others. And you tend to know, with time, which kind of person you are. If you aren't very good at it, get help! It is something you can get better at with a little training and understanding.
Beautiful scarves have beautiful colors, whether they are trendy or classic, timeless colors.
Finish- The main thing to be concerned with when it comes to finish is the stitching used for the edges. There are folks out there that like hand rolled hems. Hand rolled hems can still be done improperly. I have found this to be the case even with extremely expensive scarves (costing hundreds of dollars). When done improperly, the fabric may not be flat enough as it approaches the edge and/or the stitching (thread) can come undone fairly easily. I actually prefer a well executed top stitch, as it can give you a flatter, cleaner result.
There you go. I wish I had this information when I started buying scarves. Practice makes perfect! I'm also glad you can benefit from what I've learned!