Interesting discussion I had with a very successful science fiction writer who was also an editor for one of the largest science fiction and fantasy publishers (and what was, at the time, the highest-paying short story market). The discussion centered around what markets to sell to and what publication credits to mention.
This editor's advice was not to sell to any market that didn't pay professional rates. Under no circumstances publish in a non-paying market. He also said that he was not only unimpressed by submissions accompanied by non-professional publishing credits, but that it immediately told him that the author either couldn't sell to professional markets or didn't even believe her own work was good enough to warrant professional pay.
I've thought about it since the conversation, and I think he makes some good points, though I am not quite as strict in my application of the advice. I've decided to target professional markets first, and then go to semi-pro markets if I can't get the professional markets to bite. I won't mention sales other than to professional markets in my submissions or queries. I already wouldn't submit to non-paying market so that is no change to me.
How do the rest of you feel about this?