[T]he clear prevailing opinion is that publishers don’t know how to interpret independent publishing efforts and, most of the time, trying it does an author’s chances of selling that book to a publisher much more harm than good. Most agents responding said they really don’t want to try to peddle a book that has already been self-published unless it has achieved pretty extraordinary success.
(What’s “extraordinary”? One UK agent suggested that it would take at least 50,000 sales to get the attention of a British publisher. An American agent said in that market the number is about 100,000.)
–Mike Shatzkin on going trad.
Note that he’s talking here about getting an existing selfpubbed work picked up by a publisher, not someone who’s previously been self-published selling a new work to a publisher.