I received an email a few weeks ago asking this question, and quickly found myself composing an answer. So, if you find yourself wishing to know, here goes.
I have cultivated people whose opinions I respect, who I think know my taste and can be relied upon to recomend books I will truly enjoy. Buying books, I've come to recognize certain publishers and imprints that have lists I feel are very strong. After buying and reading several strong lists from Candlewick, I'll read anything published by them- even a YA novel on angels (which I really enjoyed, but never would have picked up on my own). Recently, I've been picking my way through my local library's graphic novel shelf, pulling anything published by First Second. Last winter, in the course of two weeks, I read three books by First Second, looked at their author/illustrator roster, and fell in love. Publisher reps recommend and hand me more books than I can ever hope to read. Some are announced as "the big book of the season," some are by authors I love, and others are virtual unknowns, handed to me by reps, read over lunches, truly enjoyed, and eventually hand sold in the store. Talking with people at a children's literature conference recently, I emphasized the importance of recognizing the merit of a book even if I didn't enjoy it. I can recommend and sell books I don't like if I think they have literary merit and there is an audience for them. In grad school, I think this is the main difference between people who have only read children's books for enjoyment in the past and those who work closely in the field- we who work in the field can personally detest a book, but realize it's importance or it's selling power. For the others, this is something that must be cultivated.