Cheap, scratchy Raschel lace is the bane of any good Lolita's existance. Being able to discern good lace from bad from just a picture on the internet is a very useful skill, being that most EGL shopping is done online. It's also helpful when you're a Lolita Seamstress trying to make quality goods for sale, or personal wear.
Firstly, we analyze how the lace feels. This isn't necessarily possible over the internet, but when you're shopping at your local crafts store, it's a must. You or someone you know will be wearing this, it needs to feel soft, or at least wearable. The number one problem with bad quality lace is that it is itchy, scratchy, and just overrall unpleasant to wear. The softest lace is cotton lace, which is only slightly more expensive than the other types of lace. There are some synthetic laces out there that are mostly soft, and they are usually more or less acceptable. Some pickier customers won't accept anything but nice lace, though. Most eyelet lace is cotton lace.
Secondly, we see how it looks. This is almost as important as how it feels, as many lolitas love to post their pictures on the internet after they've gone out with friends and had a jolly time, most of the people who will see their choice in lace (and care about it. Face it - Most non-Lolitas don't analyze your lace) will be on the internet. Generally, when the lace looks stiff and sticking up at all angles, it looks like cheap lace. Also, the thick-looking lace that looks like it comes from someone's grandma's curtains generally doesn't look good on an outfit. I always admired lacy curtains, but they're curtains, not clothing!
Thirdly, and sometimes the easiest, is to read the materials list. On most websites, they list the materials used, and occasionally even list the type of lace they use. Raschel lace is typically a no-no, cotton lace is good. For sites that only list a general list of materials, usually when they just say cotton, that includes the lace, too.
Fourth, and this is probably the best way to learn, is to contact other lolitas and ask them. They can show you many examples of good lace and bad lace, the likes of which would absolutely choke this article. Ask lolitas whose style you admire, who you see as being very experienced, and have been involved in the style for a while. Most of them are more than happy to prevent you from buying a disaster!
Lastly, if in doubt, check the pictures! If you still can't tell, then you might have to pass. If you don't mind having "bad" lace on your dress, then go ahead.