Nathan, in the under $1k range, and even more so in the under $500 range, three things come to mind.
1. Parallax. All optics have at least a little, but the cheap ones, especially variables, have more and more. Most of the $1K plus optics have adjustable parallax. This also gets magnified the larger the mag range is. 2-7 and 3-9, at 3x are decent for the most part. When we get into the 5x and 6x mag ranges, especially in the sub $500 range, the parallax is significant with a lot of optics. Some brands so better than others.
2. Repeatability. This is in the adjustments, less so in mag range than in adjustments for windage and elevation. There are two issues...spin the knobs one way, then back, does the crosshair return to the SAME exact position every time? Cheap scopes, no. Then there is recoil. A more robust and durable scope is going to not have shift of the reticle within the tube, and therefore maintain zero shot after shot. Cheap scopes are more prone to shifts than more expensive scopes. Again, variations from manufacturer to manufacturer.
3. Durability. Will it take the recoil, the drops, the temperature swings? The higher the build quality and strength of the system, the better. If you have to use the warranty, I am not interested.
There are brands whose top end optics are excellent and whose bottom third, where 70% of their sales are, need that warranty all too often.
Still, I'd bet a dollar to a doughnut that 90% of the public buying scopes have no clue when it comes to repeatability and parallax. Even when given "free" information that they can go and test on their beloved optic, they don't, and will continue to push the brand they own without regard for actual quality and performance.
I have been sponsored by Burris for years, and I used Burris optics for years before that happened. But I also keep myself educated on the current topics in optics and what the other companies are doing. I buy optics from other companies to run box tests and parallax tests. (Usually on sale, then I sell them afterwards if I don't keep them). I tested a product for Burris and sent it back and told them to fix it. But I have also suggested Holosun, Nightforce, Kahles, and other brands when they have a better product for an application than Burris. I am a working man and I'll not be affording a Beast, I want to keep it real and look at value for dollar for application. We work too hard for our money to waste it. Cheers.