How Can a Startup Safeguard Against Illegal File Uploads in a SaaS Environment?

As a startup offering a SaaS product, we're concerned about the potential for users to upload illegal content, like child pornography, under false pretenses, such as claiming it's a logo for their project. Even with public resources and access constraints, users can exploit our upload capabilities. If someone were to gain access through an invitation from a paid user—potentially via spoofed emails—how can we protect ourselves from becoming complicit in hosting such content? Is this a legitimate threat, or do malicious actors have easier methods available to them? We recognize that liability could arise even if we aren't aware of illegal uploads, so we're seeking advice on best practices for mitigating this risk.