Pheel, I personally would not buy any fish that I have not seen eat. I also usually keep copperbands and all fish over two years.
(One was 18)
If you visit some of the places where these fish are collected you may be surprised at the conditions they are kept in and how some of them are caught. The ones that are not sold are often eaten. I have seen lookdowns, tangs, angels and moray eels for sale for $2.00 a pound.
I try to buy net caught fish but no matter what they are advertised, it is pot luck. I also research any fish that I am not sure about. I recently went on a diveing trip to Tahiti mainly to learn about moorish Idols. I have seen every fish that I have now in the sea at one time or another. (except my bluestripe pipe fish) I try to see what it is eating and if it is living in mated pairs. I also try to pass this information on to other aquarists and aquariums.
You can only try, sometimes you will get stuck. Many times I bought a fish only to have it die in a few days, should I abandon the hobby? I also eat fish almost every day and I know that for every pound of fish I eat there were hundreds of trash fish that were killed and discarded. It is what it is.
Have a great day.
Paul :beer: