As a business owner as well this is my take on the whole situation. IF you bought everything from them, and IF they recommended the products and told you what you needed and said that you can powder coat the part then they by all means SHOULD take the parts back. They were obligated in my mind to tell you the pitfalls of powdercoating that part. If I sell a customer a system and I miss something then I DO NOT get to charge that customer for that part that I missed. I just deal and make the customer happy. I think that they should take the part back. Sounds to me like all they had to do was open up the holes a bit before they powder coated the parts.