I'm a sourcing professional for a fortune 100 financial institution and often use reverse auction tools for my daily job and think this is very well structured. Appreciate the communication moduled used and all other aspects to protect the bidding process.
One suggestion, when searching for shippers, allow users to query by more field. i.e. allow people who would like to search by service providers to query by location, type of product they ship, etc.
Other than that, it worked great.