That someone wouldn't be liable if they distribute the source for their modifications doesn't increase the risk, it decreases it by providing an alternative to paying damages for infringement that they otherwise wouldn't have, since the GPL author will typically accept compliance in lieu of monetary damages.
And the easiest way to violate them is simply to have installed more copies than you're licensed for, which is an issue the GPL doesn't have.
Do they preface with a "I'm not a lawyer" disclaimer and claim that anything they say is non binding?
Without those assurances, and without investigating the project myself, I’d probably turn it down too.
Support contracts can be very lucrative.
I work with a company that generally stays away from open source software, unless they have an in-house developer that can maintain it.
Most open source projects (unless it's backed by a huge company that also charges for support) are run by volunteers that have a day job. This means that support will be non-existent beyond what the developer(s) feel like and bug fixes/updates may or may not happen. This doesn't work that well when a company relies on this software for any critical task.
Especially since we're still suffering from it. There are enough project & program managers who see the words "open source" on an engineering document & send us back to build or buy some alternative.