Any retailer, be it local or online that makes any sort of conclusive statement that they don't do it should be viewed with skepticism.
I'm certainly not saying that all retailers do it, but more to the point they don't have any control over it. You often get lied to because in the eyes of an aquarist who just learned of the practice, to hear a store say they have no way to know is just like hearing... "yah, in fact I have some cyanide under the counter here!"
When you consider the way fish are collected and imported, the fish change hands so many times that it's nearly impossible to guarantee that on the part of any dealer who sells fish from the areas plauged by the problem. Ultimately, it's the locals that do the actual collecting that use the cyanide, and usually by the time the fish has made it to the actual importer, he has no way of knowing. There are organizations as mentioned that strive to prevent buying from those who use it, but again, it's difficult to prove it because it's usually done by sole discretion of the collectors, and often not the knowledge of their employers. These guys are paid by the number of fish collected, and they don't exactly have a great deal of honesty in often impoverished nations when it comes down to putting food on the table. You'd be surprised how little the actual collector gets for bringing in a $100 Naso, etc. Each time the fish changes hands, the price goes up. You are paying everyone down the line when you buy the fish for the last time.
The Phillipines and Fiji are the two areas where cyanide is employed most heavily. The three areas where it is almost never used is Hawaii, Florida, and the Red Sea. Any fish imported from the Phillipines and Fiji are highly suspect to being cyanided, but certain fish more than others. The two types of fish most often caught using this method are Butterflies and large Angels. Other fish, such as clowns, damsels, gobies, blennies, lions, etc are almost never caught this way. Sodium Cyanide is expensive, and the collectors will only use it on fish that are hard to catch any other way.
Unfortunately it's nearly impossible to prove it was cyanide that did your fish in, and often it takes a month or more for the fish to die, past any guarantees or recourse you are going to get from any retailer. Heck, it's not even guaranteed that a fish caught this way will die at all.
I have purchased many fish from this site that are heavily suspect (due to what species and what area they are from). I have only had one die that I am pretty sure was due to cyanide. Most of the fish from this site do well and thrive.
At the end of the day if you are in the hobby long enough you will encounter losses due to it. It's more or less leakage that you need to suck up, and fight by increasing awareness and do what you can to deny businesses that in one way or another willfully engage with people known to do it.
