imagine this...multi carrier style....2 carriers have you posted to an area....
first carrier texts you....bidding on a load now...
2nd carrier calls...........bidding on a load op...
1st carrier ..................dang we loss the load by a nickle to a low ball carrier
2 nd carrier calls........We got that load!!! LOL
Most carriers who participate in the multi-carrier style don't operate this way, and so this is mostly a fictional scenario that is generally spread by exclusive carriers and their drivers who don't necessarily know better.
While I agree that carriers that normally participate in the multi-carrier style are smaller carriers and "bottom feeders" as has been said here, they are completely aware of the potential for this issue, and so handle the bidding process by contacting their driver FIRST, and saying, "Hey, there is a load from Laredo to Memphis picking up at 13:00. Do you want me to bid on it at X rate?"
Then they bid and let you know if you get it. So, the scenario would ACTUALLY look like this:
first carrier texts you: load from Laredo to Memphis picking up at 13:00. Do you want me to bid on it at 0.60/mile?
You: Sure.
2nd carrier calls: load from Laredo to Memphis picking up at 13:00. Do you want me to bid on it at 0.55/mile?
You: No thanks.
1st Carrier calls: We got the load! (Or not, but at least you didn't bid against yourself.)
Also, if the second carrier calls and offers to bid the job at higher than the 1st carrier did, you then have the option to say yes to the second carrier, building your rep with them while knowing they're unlikely to win the bid. But IF the first carrier doesn't win because the shipper had a bad experience with them or something, and they go with second best rate, you may have actually bid yourself up, and got a job you otherwise wouldn't have with a single carrier.
That said, most of the big guys get first crack at a healthy portion of loads before the smaller carriers ever see them. Panther, Load1, etc are all going to use their own drivers before they put a load on a bid board, so working for a large carrier definitely has upside. Especially if they take good care of their people.