First, the side note:
If a dispatcher has "locked in rates" you may want to check to see if he is double brokering.
There is a very fine line between legal dispatch services and the Not Legal double brokering.
A dispatcher can only find loads as a representative of your MC?DOT and the carrier is the one to hire said dispatcher.
My opinion on a dispatch service right now in our industry:
In short, it takes 10, 20, 30 calls sometimes and a constant eye on the load board to get acceptable rates right now.
I don't think a dispatch service could provide that kind of time commitment for each of his clients. Its possible they may short change you on the rate search while trying to increase their load volume.
For the record, I am a supporter if the independent dispatcher type service, only if their commitment is with the carriers well being as far as rates and expectations.
A good dispatch service won't be cheap and a bad dispatch service will be too expensive, whatever they charge you. I regularly hear experienced O-Os talk about running the lanes they know best or they find a few regular customers in a few lanes and run those trips over and over bypassing the freight brokers. I don't want to think about trucking 24/7, that's why I've only wanted to be a company driver. Good luck