See this is exactly why I would never use one of the brokers, even if they were the same price as renting from an individual. It's not just about cost, it's about service.
When you're renting from an individual, everything is negotiable because you're dealing with an actual human being and not a company that has to have fixed policies. As an owner, when I rent out my points, I always allow people to make changes (within reason). And if they need to cancel, I offer them cancellation terms that don't leave them completely screwed if their plans have to change. Not every owner offers those terms, but many/most do, and if someone doesn't, you have the option to say "no thank you" and work with somebody else.
There's huge peace of mind of having someone's personal email address and phone number so you can fire off questions like "hey, how do I make sure I get free parking at Epcot," or "hey, how do the pool wristbands work at Aulani" or "hey, do you recommend renting an umbrella at Vero Beach?" Renting from a good owner doesn't feel like a business transaction, it feels like making a new Disney friend.