If you launch a competitive bid process and receive a number of RFPs, push your evaluators to articulate why they favor one firm’s proposal over another. Always ask evaluators to rank and to justify – it smokes out biases, lazy thinking, as well as on the one hand, on the other hand.
On the positive side, when evaluators grade 1, 2, and 3 on proposals and state their reasons for the comparative ratings, they inevitably move toward convergence on the relative importance of different attributes and how they spot and rate those attributes (See my post of Aug. 15, 2008: competitive bids with 35 references.).
An additional benefit of transparency and sharing of ratings is that the next time you seek proposals you will ask questions that are more precise and more germane to the later evaluation.