Remember, you are creating a writing instrument. You are NOT creating a refill. I have had this discussion dozens of times with prospective customers-if you put a Mont Blanc refill in my European pen, will it write like a MontBlanc? (You'll save hundreds of dollars, the refills are about $7.00)
Conversely, if a refill I supplied goes bad, they understand that is not in my control. Simply providing them a free replacement (I carry Cross refills, on the blisterpack), makes them "Happy campers".
In fact, it has sold a few additional pens-they agree I am still selling them a really nice looking writing instrument and they can get the refills at Office Max, Depot, etc.
Take the blame for things you CAN control, refills and wood cracking are things you cannot control-tell them this up front!