I’ve not bought any hive boxes for well over ten years now, but generally bought Thorne’s seconds. Disagree a teeny but with JBM, in that the occasional part had a dry knot or a little warping that needed attention. But nothing that could not be fixed - or exchanged, if not considered good enough as a ‘second’. I screwed all my hive boxes, so I have a pile of nails somewhere.
Frames, in particular, were always a bit of a lottery when buying seconds. Could be as good as ‘firsts’ but usually needed some selection or fettling. Still good value, all the same. I never bought many 14 x 12 boxes, as they were less of a saving (or in short supply). A home made eke, screwed to the bottom of the box, easily converted deeps to extra deeps without too much weight penalty.