What actually separates precision shops
Look at metrology capability, temperature control, tool management and how first articles are handled. A shop with a CMM, documented gage calibration and formal first-article reporting behaves differently from one that measures with hand tools and hopes.
Quality systems
Registered quality systems matter when your customer or regulator requires them. Ask which registrations are current, what scope they cover and whether the shop has experience with the specific documentation your program demands.