There has always been ambiguity in that area. In the past the rule of thumb was that collectors were able to sell parts of their collection, generally up to about 6 firearms in a year. The collector would have to show they were selling firearms not recently purchased, which would make them straw purchasers under current law (and regulations). The ATF has typically relied on vague regulations so the burden is then on the seller rather than than the ATF to prove they acted legally.
