People unable to attend

Hello Zoho Show support,
Thanks for your help previously.
We are having a particular problem more and more often and we are wondering if it can be addressed.
Often we find that a remote attendee cannot access the show. At times we have had people with the courage to turn off the protection of virus scanning and firewall and they have then had an easy entry to the presentation.
This is not always the case, but usually.
It feels very unprofessional to ask a potential client to turn off his firewall as we could (if he doesn't know us better) be accessing his computer.
Is this an issue for others?
We find zohoshow to be the perfect tool but this is just a niggling issue that won't go away.
Looking forward to your replies
Andrew