Something similar to what law enforcement uses to do a criminal history check that reports ONLY firearm owning disqualifications in your state wouldn't be hard to do. For example in Texas, felony convictions with the release/end of parole date less than 5 years, a family violence conviction, or an active protective order. And a drivers license to establish state residency would be the other part. There are a few other things that would need to be added from the feds, but it wouldn't be a huge database pool their checking against. All of the above information is complete public record, and based on open court records not some hidden watch list. I for one would be fine using something like the above when I sell a gun to a stranger. I have passed on sales before due to them "not feeling right," and something like this would be helpful. For those concerned about it tracking "who is buying guns" that could be very easily defeated by simply running random queries, to complete screw up the list of folks being queried.