sales app with 10 sellers, how to organize the separate answers from the ten sellers in spreadsheets marked with sellers’ names?
There isn’t nearly enough information here to answer your question. Try rephrasing it as though your audience doesn’t know what you’re talking about.
If you don’t want to show one seller’s data to everybody, you should use either slice or security filter. If the data is not sensitive, you could use slices. Is this the case?
When you want to manage answers from 10 sellers in one Sales app, you would normally consider one database table for all of them, then if you need to view them separately as Aleksi suggested you could use Slice or Security Filter.
Having separate spreadsheet for each seller is more aligned with traditional way of working with spreadsheets where you tend to separate each group of the same type of data into a different tab in order to organize them or have them in separate views. That approach does not work for a database app.
I recommend reading this article about app design: https://help.appsheet.com/app-design/app-design-101 help.appsheet.com - App Design 101 App Design 101 help.appsheet.com