Contractors care about their reputation with the planning department.

That can include roof, water heater, HVAC, plumbing, electrical, mold, rot, warped floor boards, bad foundation, termites, sink holes, fascinating animal occupants, bad reputations (that was a drug house or had a fire or was used for other things that I don't want to mention), and so on.

Yes, it costs a lot to go with REI Nation, and the cash flow is low, but they have an excellent reputation.

Anyone know an inexpensive and reputable structural engineer? 

I'm known in my market as an investor-friendly Realtor, and people bring me deals based on this reputation.

Where have you successfully found reputable, investor-friendly lenders in the past?

They will still match you with CPAs with KNOWN poor reputations and a long history of client complaints/issues as happened with me. 

My recomendation to you is to talk to a few reputable property management companies first, check the zip codes/ areas they work and then start your research from there. 

Many of the tax professionals on this forum are not "cheap" but can make a good fee for fixing situations where investors relied on poor advice from cheap advisors.My conclusion is to interview a few and go with a professional that you feel comfortable with no only their fee, but also their personality, their experience, their reputation, and their willingness to not only advise you as you start your journey but provide education and planning for what type of investor you want to be. 

And how would I go about finding a reputable builder.