Some vendors are good at marketing and sales. They prepare polished RFP presentations. But they're not necessarily the best choice. Because of this, you've got to know what to look for in RFP responses...and it goes beyond just assuring that they complied with the RFP request. Some of the best and most cost effective vendors won't respond well to an RFP.
And you may have to help them provide the information you need to select them. But what you want ultimately is the best solution for your company; you want to avoid selecting the prettiest RFP as the best.