remove.bg is basically the go-to for background removal, and the free version works pretty well for most photos. you just take screenshots from the website or download the app, send the photo and done - you get the image without background in decent quality. there's a daily request limit on the free version, but for selling stuff on Marketplace it usually gets the job done.
another option is pixlr, which has a free online editor with an integrated background removal tool. it's not as automatic as remove.bg, but you get more control if the photo has tricky details. i've used it for small products and it works fine, though it does require a bit more patience.
if you want something more powerful without paying, gimp (desktop, not mobile) removes backgrounds for real with professional quality, but then it's more work and you need to learn how to use it. for speeding up marketplace sales honestly, i'd go with remove.bg or pixlr - both free and not too complicated.