I am just guessing here, but the added cost to you, the final purchaser of doing a trial piece for every part, would just raise the price of the finished product, and just extend the timeframe before the part was available, the quality of the parts can be seen from the previous examples shown earlier in the thread, if the producer is confident that the part will print correctly, from previous experience, then the first buyer can often get a reduced cost by being the 'beta tester' (if I read the shapeways website correctly). the designer only gets paid when a product is printed, so he has to take a chance with his time spent CADding up an item, that people will want it and buy it.
Grendel