You are confusing Gross and Net. You don't pay taxes on...
You are confusing Gross and Net.
You don't pay taxes on Gross. Your costs incurred are part of the P&L. When you sell something "at cost" and "don't make a profit" that is Not removing it from Sales. It is Gross Sales income for you, and then you Pay someone = your expense.
I buy $100 of Stamps and charge you $100. That is my $100 income on the P&L, $100 Expense on the P&L, and the Net Income is $0. The reporting does the math or Net; you are supposed to track everything that happens as Gross. And if my selling you products such as Stamps is subject to Sales taxes, you will be charged Sales Taxes on this sale of goods or products.
"I am thinking this would be treated similar as selling tickets on consignment."
Not really. Unless you have a Trust Account requirement, it is unlikely. You should always review all of your accounting and operational activities with your own accountant. No one on the internet even knows where you are located or anything about your business.