I've been on poshmark for 5 years. It's a good place to sell your stuff whether kid's books, toys or clothing. Easy to use website. They are quick to pay you when you made a sale. Also you can find there unique things for a discounted price. So far I have not encountered any problems with. The customer care was also quick to respond when I had a technical issue.
I didn't have to return anything, but the website says they refund if you got counterfeit or not as described.