Subcontracting hardwood work — finding qualified installers

I'm a GC who specs tropical hardwood on about 10-12 projects per year. My biggest challenge is finding subcontractors who actually know how to install it properly. I've had two bad experiences this year — one guy used galvanized screws on Cumaru, another didn't pre-drill and split about $800 worth of Ipe boards.

Does anyone have advice for vetting hardwood subs? Are EHCI-certified installers available in most markets? I'm in the Chicago area.