Acquisitions Colleague Whose Pre-Occupation with Likeability Hamstrings Negotiation

Hello all - I am dealing with a situation, and was hoping to hear from other with the same/similar experience.

I have an acquisitions colleague who is great at sourcing leads, because he (a) tells people what they want to hear, (b) only sees the upsides in deals and never the downsides, (c) is completely non-confrontational and (d) is a great schmoozer.  In short, it's all about likeability for him/her.  

The problem is that once we're past square one, it's impossible to negotiate because he establishes a buddy-buddy relationship with all parties and won't push back on deal terms, and won't call people out when they've reneged, changed economics, told half-truths, misled, etc.  Me being the 'curmudgeon' colleague, I have to ask questions like 'what is the tenant credit?' 'what is the zoning?' 'is there deferred maintenance?' 'what are in-place leases?' Sellers/agents give non-answers that suggest there's an inconvenient answer (bad tenant credit, wrong zoning etc etc), and the nice-guy acquisitions colleague accepts these answers (and counterparties only want to deal with him/her as a result).  Predictably, these makes for huge issues down the road during due diligence.  

How have others dealt with the situation?  Does it only work if people-pleasing acquisitions folks are relegated 'sourcing' roles rather than negotiating/closing?  I don't have the authority to force that arrangement, but curious how others manage, as current situation doesn't feel sustainable, but surely there's a place for the non-confrontational people-pleasers.  

TLDR: how to deal with colleague who is too nice/non-confrontational to negotiate?

TYIA