Well, opinions are like, umm, noses -- everybody has one. In MY opinion, the potential buyer who has been denied may have committed a crime, especially since they signed the 4473 and verified that everything they entered was the truth under the penalty of perjury. The gun store needs to protect itself against any possible culpability in selling a firearm to a prohibited person. I have no problem with the clerk taking notice of appearance, and I'm sure that the system contains errors that might result in a false denial, but how is that to be determined?
We rail against background checks because even if a potential buyer is denied, few are ever prosecuted. How are they to be prosecuted if the police are never made aware that the attempt was made?
I can't stipulate that every dealer works the way mine does, but my dealer is incredibly professional and does not have "minimum wage keypunch operators" entering the data from the form. As for how a store treats its customers, how else should they react when a customer commits a crime? Is there a difference between shoplifting or committing perjury? Should they not both be investigated by the proper authorities?