CruiseCompete.com is a good resource. It gives you a base price to use to compare other offers.

CruiseCompete.com shows rating information for its bidders. BUT do your own check at bbb.org.

I prefer using an agent I know but if the price savings are real and the bidder rated B- or better, I'd consider Cruisecompete.com's bidder. If less than A- I'd carefully look at how complaints have been handled.