First, let me say that my clear fave is The Timeshare Store. I have both bought and sold with them, and they are the best in my book for product/market knowledge and professionalism.
Having said that, there are four brokers who more or less specialize in DVC resales. I don't think you will have any ethical/trust issues with any of them.
It is important to understand that all of them are regulated by the Florida Department of Business and Professional Regulation, and all of them are held to exactly the same high standards Disney itself is held to. The timeshare sales/resale marketplace in Florida is very tightly regulated and is a very clean market.
IF you have an issue with some of the brokers, it will usually boil down to one of two causes: spotty to poor customer service, or a problematic seller.
I have never dealt with Fidelity, but based on dozens of anguished threads since their inception as GMAC, the description above of "hit or miss" sounds about right. There was a time when they were pretty clueless, but they have progressed to "hit or miss." One of the other brokers who I have dealt with (but cannot mention) also gave me "hit or miss" service.
The Timeshare Store has always excelled in customer service for me in the five transactions I've done with them.
Problematic sellers can be difficult for any broker. The better brokers do sound due diligence to try to identify them and resolve issues up front. Other brokers don't. But a problematic seller can lie, or they can just be stupid, and there is little the broker can do about that -- except to try to fix it quickly when the problem surfaces.
Unfortunately, because they have a business arrangement whereby DVC refers owners wanting to get out of DVC to them, Fidelity tends to get the lion's share of the problematic sellers -- people who don't understand what they bought, own, or are trying to sell; people who are so deeply underwater they can't pay in enough to complete a sale; the list of issues goes on and on and on.
Professional brokers sort through those situations pretty easily; others don't...and it's YOU who are handling the stress of the saga.