Absolutely. But the fact that your specs are met is actually proving my point.
Part of ESMC's "secret sauce" is the relationship you've created and your ability to properly manage requirements and specifications. Your manufacturer has probably learned that they can't "close enough" you.
My primary contractor in China (previously Hong Kong) always has been good to me and at times bent over backwards if the need for a last minute change was required and at no additional cost. For example, I used to source BLMA Ride Control trucks for the X58 family of cars through BLMA and later Atlas that were molded at the Affa factory and sent directly to my contractor's factory - economically and scheduling-wise the best option as the two factories are within 20 miles or so of each other. But I had no control over whatever Affa delivered. Given that they made numerous trucks (and truck bolsters) for everyone, they once sent ASF trucks with the proper side frames and the proper height bolster, but the diameter of the bolster hole was smaller than expected (not to mention the shipment was late). My contractor drilled out the holes of the trucks at no additional cost or delay to me, even though they had to create a fixture to do it. That was the primary reason for tooling our own ASF truck frame and machining our own wheels. They also drill the grab iron holes in the X58 roof for the high-brakewheel no-roofwalk variation, and made that fixture at no additional cost. Nowadays, there is an occasional additional cost for unexpected situations but it's never excessive.
Ironically, my first project with my primary contractor was them stepping in at the eleventh hour to paint/deco the last run of the passenger car sides, when the domestic contractor who had done the first run and had committed to doing the second run simply decided at the last minute not to do it. That was after the parts were molded (domestically) and paid for. So that's how I ended up contracting in China. I started out domestically, but was
forced overseas. And the painting/printing on the second run of the passenger car sides was light-years better than the original run produced locally. I wish I had contracted with them on the first run of sides.
I also tried to have at least one model tooled and produced domestically, the GSC well car. But the quotes I got were considerably higher than what it cost to tool the six-variation X58 model. And the GSC well car is a snap-together four-part plastic and diecast body, with MTL 2004 couplers and Affa-style trucks. As opposed to the X58 with three body variations, two underframe variations, etched and wire and plastic detail parts that must be cemented in place, and etched coupler plates with screws to go with the MTL 1015 couplers and Affa-style (now ESM) trucks.
How do you avoid the situation where the pre-production samples were acceptable, but the mass production units were found to be substandard?
Do you employ an independent source inspector at the subcontractor's factory to catch any problems before the production order units are shipped?
I've never had that scenario occur, even with the handful of other contractors that I've since moved all work away from. To be honest, most of my past issues have revolved around scheduling delays, or cost increases, or the contractor not wanting to manufacture my minimums. But never with my primary contractor, and I've never had quality issues, with tooling or with decorating, with any of them.
With my current contractor, I get physical paint sample body shells first (for any new colors being introduced). Then I get hi-rez photographs of decorated bodies to approve, which starts production. Then I get physical final packaged approval samples while the cars are being painted/printed/assembled. Then final packaging starts.
On new tooling, I first get at least six sets of test shots from the molds of the parts on the runner, along with samples of metal-stamped, diecast and etched parts. I use this to assemble and test the model, to uncover any needed corrections. Then I get an assembled pilot model with trucks/couplers and painted a color that shows all the details, which I check for assembly issues and then road test. Any needed changes are made and then another assembled pilot model, painted a different color, is sent to check and test. This cycle continues until all issues are resolved, and usually takes no more than two cycles.
So the "secret sauce" is finding a contractor who is reputable and with honor.