As far as the feds are concerned, as long as you're not "in the business", you're OK, and these buybacks tend to be rare and one offs. In practice and from their viewpoint, the first case of valuable guns is OK because there don't tend to be too many of them and there can be many different people doing this for any one buyback, in the latter case it tends to be FFLs who play that game since they can easily have a collection of junker guns they've bought but that didn't sell.

In some non-free states, you cannot legally transfer your property to another private individual.