I've never had or even looked through a bad scope, but I did recently get a lower end Bushnell banner 6-18x50 that's not too bad for the price I paid. Cost about 100.00 it currently resides on my m11 savage in 223. Overall it's a decent scope, there is some edge distortion at higher magnification 16x and above, as well as being a bit darker at higher magnification levels, but for 100 bucks it's a good trade off. I regularly shoot this combination at 300 meters and am able to see 223 holes in the non shaded areas of the target.
I prefer higher end optics, bought my first Burris ff2 4.5-14x42 when my low end Nikon bushmaster 2 blurred out. The Burris, 200 shipped, is good quality, not as good as my monarch 3 or vx3l 3.5-10x50, but very good.
Recently told my SIL I was going to spoil his eyes from buying "cheap glass" by giving him a Bushnell 3200 elite and a Leupold vxii.
Buy good glass your eyes will thank you in 30 years.