This app was mentioned in 5 comments, with an average of 1.00 upvote
Depends on what you are looking to sell, really.
I've had a lot of luck with these two:
Mercari https://play.google.com/store/apps/details?id=com.mercariapp.mercari
Vinted https://play.google.com/store/apps/details?id=com.vinted
And then of course eBay and Amazon.
if i download on android phone does it still count? https://play.google.com/store/apps/details?id=com.mercariapp.mercari
Try Mercari. Use paypal.com/shipnow to avoid Mercaris overpriced shipping labels.
https://play.google.com/store/apps/details?id=com.mercariapp.mercari