Hiring experts when you are not one

[Maria Teo]

How do you feel confident in hiring a professional when you don't have any background to evaluate their expertise. I know it is best to start with recommendations of people you've already worked with but I'm still early in my "career" and don't have a trusted solid network established and even then things don't always work out. 

Here's my story. I have two buildings which require a soft story retrofit. For Building A, a contractor I've worked with recommended Engineer 1. As the project scope increased I hired Architect. Seems the Engineer 1 was only interested in drawing up a quick plan and moving on. So Architect recommended Engineer 2 who is a partner in a seemingly a reputable firm. Engineer 2's firm  partner works with the city on large city projects and planning. A year later, news breaks that the city is suing firm's partner for fraudulent work. Technically Engineer 2 who oversaw my plans wasn't involved though he is being dragged into the suit by extension. Architect assures me this issue with the other partner and city doesn't impact the soundness of my engineering plans.

Still I'm not keen to work with this firm again. So for Building 2 I got recommendations for other engineers.  I only hear back from one.  Engineer 3 seems honest (gut feeling) and mentions that this building should get a retrofit. Engineer 1 had signed off that the building didn't need a retrofit. According to Engineer 3 that wasn't technically wrong by the language of the ordinance, but misses the "spirit" of the ordinance, that is sufficient structural integrity. Later learned Engineer 1 never physically when down to the foundation, so I am inclined to believe Engineer 3.

The undertaking for Building 2 is going to be costly. Engineer 3 has done other soft story work, though I don't know of this scope. However I like that he isn't pressuring me to do anything quickly and seems happy to talk me through the process. It is hard to find an available engineer these days but should I still try to get a second opinion from another engineer? 

I guess my main question is at what point can you feel confident in trusting a professional when what they are doing is well outside your scope of knowledge? What is sufficient due diligence and what is just paranoia?