Don't people wipe the filter mounting area with a paper towel to clean off any dirt, etc. One should feel the old gasket even if one cannot see it. But double checking the old filter for a gasket is also a good idea.
I also had a defective filter once, so I always look at the gasket and then look across the bottom of the filter to make sure its not warped.
Do I think if someone dropped a filter at Walmart and dented it would they just put the filter back on the shelf?