When people want to know how a new camera or lens performs, many will head straight to the Internet to check out sample images. There are usually plenty to sift through. The problem is that the capture technology (the camera and/or lens) is likely to be so much more refined and controlled than the display technology (your smartphone, tablet, or computer screen) that a proper evaluation is going to be difficult.
What are you looking for? If sharpness, you can expand the image to 100% on your screen, but then the sharpness/focus of the display itself comes between you and the truth. What about color? Unless you’re using a calibrated monitor there’s no way to be sure that you’re seeing the right colors. Dynamic range? In addition to the fact that the dynamic range of your display is limited, ambient lighting and glare can easily ruin your chances of seeing the full dynamic range of the image on screen.
If you’re a pro or an advanced amateur you already know all of this, and probably have a calibrated, controlled viewing setup that will allow you to make informed decisions. You’ll also know that a well-made print is generally better than an electronic display for image evaluation, but unless your images are actually destined for photographic paper or a printed medium, you probably won’t bother.
If you don’t have access to finely tuned viewing gear a different approach becomes necessary. And that approach involves … checking out sample images on the web with whatever you have at your disposal. The trick is to look at lots of images taken by different photographers. One photographer may simply produce images that you happen to like or dislike, which will obviously bias your decision. Also try to view the images on a number of different devices. In looking at lots of samples from different photographers on a number of devices, do you notice any characteristics that seem to be common to most or all of the images? Those are likely to be the camera or lens attributes you need to consider.
You can also, and probably should, take in the opinions of reviewers or photographers that you trust. And of course, nothing beats borrowing the camera for a while, even a few minutes, to shoot a few images yourself (take along your own memory card for this) and get a feel for how the camera/lens handles.
But after all is said and done, if your photos will be viewed exclusively via the Internet on smartphones, tablets, and uncalibrated computer screens, then checking out samples in that environment is not too far off the mark. Just remember that evaluating sample images on the web will only give you a very broad sense of actual image quality, and how the data from that camera/lens will respond to processing.