well i always see people using the broadcast to do other stuff than advertise, then the message "PLEASE DO NOT ABUSE THE BROADCASTER" so, my suggestion is to use a broadcaster that has options instead of text input.
the server i played before had a broadcaster where you choose whether you want to buy, sell, trade, recruit, etc.
then, you'd input the item id and how many you want to sell/buy.
then you could either put a set price or put 0 so it would say "PM offers".
also, broadcasting was free but limited to one broadcast per hour.
for custom broadcasts, people would use donation tokens to buy broadcast scrolls.
just a suggestion, the broadcasting system there was pretty smooth, so ~(owo)~