I don’t think “real users” can be paid for, can they? I’d rather just keep improving my site/product until people want to use it without being paid.

THIS^

Make like she’s joining her friend outside so they can chat while working. Maybe even combine shops so customers don’t realize whose items are whose and buy from both shops.

There are many ways to handle this tactfully and make it a cooperative effort rather than a confrontation.

Set up your own stand outside and may the best shopkeeper win.

You can create RSS feeds in Google Sheets for free and then embed them on your website.