My favorite event is Half-Off Day at The Salvation Army. I sometimes find items with the tags still on there.
Toddlers’ clothes tend to get worn out, except for special-occasion items, so I usually buy those new at Walmart.
I get a real thrill from paying $2 for a dress I know retailed for at least $100.
Prob depends on where you live, what time of the year it is, etc etc etc. Lots and lots of grandparents in my area - I suspect that's where a lot of the consigning comes from. Grandma has a drawer full of clothes for when the kids come over, and they get worn once in a blue moon.