I have a similar challenge here, although not in-person. We welcome platform vendors to be a part of this community – they are frequently veterans in the community space and have a wealth of knowledge – but I don’t ever want community members to feel sold to, either.
I handle it fairly loosely by touching base with vendors when they sign up, welcoming them, and explaining that we value their general contributions and welcome comment on their specific products but only if they go to directly answering a question. I’ve had one debate with a vendor that called me short sighted (he didn’t return), but generally I think the personal contact and setting clear boundaries has worked. We don’t have formal guidelines because they haven’t been needed.
Can you test the waters with just one or two partners at an event to see how it gels?
@HelenSilby will have useful insight. Helen, how do you manage the balance between vendors/partners and community when you run events?