Selecting the supplier capable to manufacture the product must be based on capabilities. Seldom a supplier, when asked if he can manufacture the product, will say no. The result is often a long period of learning mostly paid by the customer. Better solution is make a supplier selection based on the seperate part failure rates (yield) and look for a supplier capable of making those parts. It’s most of the times more complex with supply chains with one or even more tiers in the chain. This comes with the same restriction for selecting the supplier.
The most difficult part is the part failure rate or yield. Starting point is failure rate achieved in the past. Another chalenge is the Technical Product Documention where the split up is made for between the different disciplines like optics, mechanics, electronics, mechatronics or gas and fluids. Try to have as little overlap between disciplines. There are very limited suppliers which can do them all.