I am looking into buying a duplex in Hyatt Park and wanted to get some advice on what contractors/suppliers I could contact that have investor friendly pricing for kitchen cabinets, countertops, and bathroom vanities.

Great to meet you.We source from four primary suppliers: Lowe's, Home Depot, Floor & Decor, and Amazon.

But it seems to me that referral clubs only real value is vetting suppliers.

Not to say that you'd pick crappy materials, but contractors with experience have manufacturers and suppliers that they know guarantee their products and that helps them know they can stand behind their work. 

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They don't rely on ONE supplier, ONE broker, ONE anything.  

If you are the lone supplier of a specific housing product and there's pent up demand you will absorb your units quicker and have tenant stay longer given the lack of alternatives.

I found through a referral a great supplier that can provide new, and not scratch and dent, for about what I would pay for used.

And all suppliers and subs are current as is the customer .  

Plus, building those relationships with contractors and suppliers while gathering numbers can lead to better deals down the road.