Real estate groupreal estate sales

I recently had an agent & his rep list my home for sale …during negotiations I told them I could only pay for advertising ‘on sale ‘ they did not reject this…(they’re rip off merchants …what do they do for their commission?) Anyway the rep wrote ‘pay on demand’ beside ‘due & payable’…I pointed this out twice saying that is not what I agreed to and he said …(and I quote) "Don’t worry about it!’ I thought that meant I would be billed ‘on sale’ as we had spoken about moments before and signed. Three months later I began receiving accounts …many letters flowed back and forth and I finished up saying I would pay it off after he gave it to a collection agency. I have reported them to Consumer Affairs in two states. If all responsibility rests with the signatory …then one can assert that no responsibility rest with the proponent ! Surely this isn’t acceptable…the law is stacked against the people …what can be done about such scum?