I've had some good luck on Close5. I have not had good luck on Varage Sale. Also have had good luck on local buy/sell Facebook groups, and Nextdoor too.
What are you trying to sell? Poshmark is a great app for women's stuff. I sell a lot on there. I've sold some kids clothes but it's not a kids site. I have luck selling kids stuff at local pop up consignment sales or Facebook groups.
Re: Buy / Sell App or sites