Ask HN: How dangerous is source code access?

For a small startup whose product requires source code access (think static analysis as a CI service), how dangerous is it having access to the (non-open) source code of commercial customers?

How do we protect ourselves from the risk of a "IP troll" trying to earn money by claiming that we have used their source code, looking for similarities between their code and ours if it comes to a court?

We are planning to have a free tier where anyone can sign up, and without any protective measure it seems that we are opening up ourselves to risk.

At the same time I realise that the situation of having source code access is common (GitHub, GitLab, Travis, Netlify, ...) - how do the big players protect against the same risk, besides having a formidable legal department?