Ever gotten money back from a machine shop?

I wouldn't give him a pass but heres what you might do. As a new business owner I'm sure he doesn't want to trash his new found reputation. Although he might not give you money back, you wouldn't be out of line to ask for an instore credit or gift card for the appropriate amount. Seeing as his machining and assembly skills are suspect I would only use the credit for parts. Also remember the internet can make or break businesses. Bad reviews are the new word of mouth times 10!!!