In a perfect world, yes we should be promoting the good ones.
In the real world though, we all use whatever competitive edge we can.
In the example I used, the shopkeeper who was so desperately curious to see where my stuff was coming from, ran a store that was at least 10 times the size of mine (sales-wise, not square-footage wise - but they were probably 4 times the size of my shop). I was no threat to him - or his business - his store (which is now out of business - after he sold it) was at least 25 miles from mine, and I'm a tiny fish in a huge pond. He was the big fish... so I still chuckle wondering why he was so darned curious about where I was buying from... but I digress...
So if I'd told him I use XXXX because they have great stuff, he had a lot more buying power, and thus, could potentially buy up all the great stuff I would normally get. Honestly chances are he already knew and perhaps used my suppliers... he used a lot of them because he did a ton of volume, and I daresay some of the smaller suppliers I use might not have been able to fill all his needs... but I digress... I saw who he was using - their logo was all over the boxes

(NO it wasn't Fishheads - at least not that time - it was before Fishheads made those Nemo boxes...)
If I perceive my suppliers as an advantage (MY perceived advantage, which may or may not trickle down to the consumer) and I truly believe that what I buy is "better" (ie more ethical, more conscientious or "cleaner"/"greener" source), then I'm going to protect that because I didn't have the big bucks or other bells and whistles that he had.
So yes, it would be "greener" to have people promote suppliers that do it right... but it's not likely to happen for the reasons I've stated. Some folks aren't as protective of their info as I am. I tend to use smaller suppliers so there's less to go around than at the big box wholesalers.
Now one could turn that around and use such info to "out" suppliers who aren't playing by the rules or doing it right, but then it would become a legal liability, particularly when some accusations (ie cyanide-caught fish) would be difficult or impossible to prove - at least at this point in time. It's much easier and safer to sing praises to a good one, than to be critical of a bad one, on that I'm think we can all agree.
And at the end of the day, some shops or their management don't care. It's all about cheapest price, best selection and to hell with how they got there or how they were collected. IMO those are the ones that are enabling less than ethical practices to continue.
I learned a long time ago that the most expensive creature is a dead one, and that all goes along with how things are collected, handled and shipped. I will gladly pay a bit more to get something that has a better chance of longer term survival than something that is likely to be DOA, DAA or leave a bad impression with a customer because one too many died after purchase.
Jenn