I am unaware that this violates any Biblical principles, but I am willing to be enlightened on the issue. We are a family, sharing with each other, bartering, and mutually enhancing each other. If I am going to hire a babysitter or buy a used car, I would rather buy it from someone in the church, than an outsider I don't know. This helps homeschoolers find the curriculum they want and helps those selling to have the funds they need to purchase other materials. I'm unaware of any Biblical principle that this practice violates.
Capitalism is a Biblical concept.
We are a family mutually edifying one another. No individual or church is profiting from this. The purpose of selling the tickets on Sunday morning is so that we know exactly how many are coming. We have had problems in the past with getting a hand count or having people sign up on a sheet and then only half the people show up and food has been prepared for twice that amount. I'll be glad to hear more on this from you, because I would think it unlikely that I would have satisfied all your concerns.