I agree, testing, adjustment, and quality assurance are in indespensable part of making fountain pens. Nothing will turn a potential return customer into a detractor faster than getting that beautiful new fp home, inking it up and finding out it won't write, or writes poorly.
My findings are pretty close to yours on overall factory fp sections, BUT I have found that by mixing and matching nibs, feeds, sections, and converters between at least 4 or 5 kits (or that many spare sections) at a time, I can bring that incidence of a "unuseable" component down to less than 1 in 10. With a little more time and a little money invested in getting the experience and tools to properly floss, adjust and modify the nibs, it's down to about 5 percent.
But no matter how you do it, NEVER sell a pen that you don't KNOW writes well. Personally the last thing I write with a fp after I finally have it the way I want it, is the description of the pen, materials, ect on the back of a business card. Then the pen gets disassembled, cleaned and reassembled, and the card goes into the case with it.
