wow, thats a really bad network configuration.
That host obviously doesn't know what they are doing. It's not cost effective to run vlans... that most likely means they are running an all layer2 switched network without any layer3 distribution. It costs almost nothing to deploy proper infrastructure. The only other cost would be the burn of IP space for your network/gateway/broadcast loss but even still that is an absolute MINIMAL cost of ensure the security of your network and isolation of potential problem customers
