I've been hobby baking for 2 years and feel ZERO guilt for using Duncan Hines as my dry base mix. Once I pour those ingredients in the bowl, I pitch the box and add everything else I want and obtain absolutely fabulous results every....single.....time......
No worries about the weather, humidity, heat, air conditioning, old leavening, cold eggs; consistent results every time. I am a hobby baker and don't plan on ever selling cakes; I freely share my recipes with anyone who asks.
IF I were a professional baker:
I would respond that my recipes are a trade secret and cannot be shared.
If a customer asked specifically if my cakes were made from a box mix or from scratch, I would tell them what I shared above: "I use a dry base mix. Once I pour that dry base in the mixing bowl, I add everything else I want to obtain absolutely fabulous results."
If that same customer expressed reservations, I would invite them to determine their preference based on taste. If I lost a customer because they wanted only scratch--then so be it, they were not meant to be a customer.
A business needs to identify their target clientele, market to that specific market segment, and maximize profit. If your target market is people who buy only scratch--then bake only scratch. If your target market doesn't care, then bake the most profitable, consistent, tasty cakes possible. If that means you use mixes, use mixes and don't apologize.