I am certainly guilty of looking at a koi bowled for someone else.
I think the important point is to not get in the way and not to insert yourself in the discussion between the dealer and the other customer unless expressly invited to join the conversation. ...I eavesdrop on many dealer-customer conversations at koi shows. I usually look at koi in a different tank while listening to what is being said. There is a good deal to be learned from answers to questions one would not have thought to ask, and even more on those occasions when the answers to one prospective customer are not quite the same as the answers given to an earlier one... sometimes the different answers are for good reasons. One gets to know the dealers whose knowledge can be relied upon, as well as those who are always pitching. When I overhear a dealer who inform an eager hobbyist that the koi exciting him should not be purchased because it will not grow as large as desired, or will not be show-worthy over size 4 ... Well, I become more interested in what that dealer has to say.