Per FAR 36.602-1(c) discussions are to be held with at least three (3) of the most highly qualified firms. What if when the solicitation is posted, there are less than 3 qualified firms who respond? What if there is only one response to the solicitation?
As background, Qualifications-Based Selection (QBS) is a procurement process established by the United States Congress as a part of the Brooks Act (Public Law 92-582; this is codified in 40 USC §1101 et seq. and further developed as a process for public agencies to use for the selection of architectural and engineering services for public construction projects). It is a competitive contract procurement process whereby consulting firms submit qualifications to a procuring Government activity who evaluates and selects the most qualified firm, and then negotiates the project scope of work, schedule, budget, and consultant fee.
You did not provide much background information in your question, but not withstanding that, here you go. The first question you must inform when less interest in an architectural and engineering services solicitation is received should be, “what happened, why did we not receive several adequate proposals?” The answer for that should be found in your market research. There may be valid reasons for the lack of interest, the engineering requirement may be unique and require expertise only found in a very limited number of firms, or the geographic location of the site may be such that it is undesirable to most if not all qualified firms. You also must consider whether the requirement was well defined as presented in the advertisement. The bottom line is, can you change the solicitation to gain additional offers? If the answer is more engagement with industry or better information will generate more interest, you need to cancel the existing solicitation and advertise under a new solicitation. As soon as possible.
Under a QBS procurement, the cost of the work (price) is not considered when making the selection of the best or most appropriate provider of the professional services required. Fees for services will be negotiated and may not exceed 6% of the estimated cost of the building being designed, per FAR 15.404-4 (b). A procurement of architectural and engineering services shall be considered in compliance with FAR direction provided in 6.102(d) (1) even when the Request for Qualification does not generate three responses as long as a good faith effort to publicly advertise and directly solicit participation was in fact made. The source selection authority shall determine whether a good faith effort was made using his or her best professional judgement. This determination must be documented and maintained in the contract file.
All this said, the contracting officer must negotiate a fair and reasonable cost for the effort and fully document this rationale in the post negotiation memorandum. This may be made more difficult if only a very few or only one offers are received.