I am not sure about proper etiquette of naming a seller. If words are the truth and not just a matter of opinion then what is wrong with the truth? True Facts remain the facts not opinion or an idea.
"If "they're in a pond w/other fish," how does a customer make sure they're getting ONLY the HPB?"
This is a difficult topic. As I know it there are no guarantees nor warranties in the fish delivery / selling business for pond stocking. This is why one has to be careful who one does business with and trust the seller to do the right thing. Mistakes can easily happen in the live fish selling business, I have had those types of mistakes happen to me which is why I mention or list precautions when buying your fish if it is important to you to not get unwanted fish.
We are dealing with live fish. Live fish can be moved around by 'Mother Nature'. If one has the wrong species soon show up in a pond, the seller can say a bird brought them into the pond or have some other excuse such as a neighbor added some free fish for you. Both are not impossible to happen. Many pond owners do not get too concerned if a couple of the wrong species show up in the pond after stocking. Proving the problem was with the seller is IMO pretty difficult. This is why I think it is IMPORTANT to let the seller know that you do not want unwanted fish in your order. Let the seller know his reputation is at stake on the national widely used Pond Boss Forum. Plus you have to pick a good fish seller and trust him especially for certain fish species and sizes that you are buying.
Another very good option is to hand sort the fish that you buy. Know what that species looks like and how it is recognized. Do your homework. Do not take the fish delivery for granted if pure species are required. Take some precautions. Buying lots of fish makes hand sorting more difficult and time consuming and often not practical. Again buy your fish form very reputable fish farms and even they can make a mistake. Risky business.
Another option as was already mentioned buy the larger sized fish that are more easily recognized by the fish seller and hopefully yourself. Common distinctly featured fish such as LMB, SMB, catfish, HSB, yellow perch, koi, crappie, golden shiner are all pretty easily recognizable. Difficult to recognize fish are the sunfishes and some minnow species. FHM are pretty easily recognizable after you see and compare body coloration and pattern from a few hundred of them. Most difficult to correctly identify even for many farm new type workers at the fish farm are the small sunfishes such as RES, BG, HBG, and now specklebelly hybrid bluegill (BGXRES). I know of some fish farms who grow their own hybrid bluegill (HBG). A HBG does not have to be the first generation of the bluegill X green sunfish cross called F1. HBG can reproduce in mom and pop fish ponds and the offspring as of F2 or F3 generation could be unethically sold as a HBG.
