There has been some discussion on eBay of counterfeit Kenko UV Japan filters being sold. They're lower cost filters to begin with but still people copy and counterfeit.
There are some excellent resources out there that compare the quality of the filters and how they impact the IQ of the images. Oddly, at least to me, while some brands were consistently rated high that was the exception with most having models that came in at the top, middle, and bottom from the same brand. I know that Hoya, for instance, has some solid performers and some real dogs among their filters based on many reviews I have seen.
Here is an excellent review of 24 different UV filter models:
UV filters test - Introduction - Lenstip.com
For example, Hoya has lenses at the top and bottom but has 3 models at the top:
Hoya 72 mm HMC
Hoya 72 mm Pro1 Digital MC
Hoya 72 mm HMC Super
But the HMC model is the least expensive among those three and rates essentially the same as the #2 which was literally twice the cost. But the Hoya 72 mm UV-0 - Standard model, which costs the same as the HMC model, rated rather poorly overall. So, maker is NOT the main factor and its important to read some independent reviews in my experience. They led me to a filter maker that I was unfamiliar with, Marumi, for my 10-24mm lens based on performance vs. cost and I have been very happy with its performance.