Or did you mean in the sense that the nursery couldn’t possibly be reputable?
I think, he finds that the nursery couldn't be reputable, unless of ill repute... as it might be difficult to find these species imported with the correct CITES-allowances and thus legal. But sometimes you, actually, see some rare species with the correct paperwork done, God knows how?
On the other hand: I don't think many of species in trade (except those from a pre-CITES lineage), that we accept without difficulties, might really hold up for scrutiny. The plants, we have, might clearly have been grown from seed in a nursery. But - I might have got this wrong - I think, the nursery owner, that sold it to us, should be able to produce evidence, that the parent(s) of the plant is (are) legit and not jungle collected?