Do you contend that the cost of labor is $0? If someone needs to handle it, there's a cost. What they charge the client for that is a different story.
I'm a TA too. I'm not going to discuss voiding within the 24-hour period now, because I think that maybe legally required to do at no charge.
But in regular cases, even if the airline doesn't charge for changes, I can understand why a TA is legit for charging a service fee for their work (I do myself). But we're discussing charging an irrational $250 "service fee". Assuming they sell tickets at a small loss, if one in five people need to change or cancel, they are still making a nice profit...
Anyway, I'm just assuming. I don't know if it's really a sustainable business model long-term. I actually doubt it.
As you yourself have made the claim multiple times, that when you compete on price, you always lose...