Brett working with an online vendor to handle things is one thing. But Brett doing all the ordering, sorting, and shipping of a bunch of shirts just to make a couple hundred bucks profit is another (and in my opinion a lot to ask).
Who is Brett?
As pointed out multiple times, Bret wouldn't have to do any of the things you mentioned. None of them.
He wouldn't have to take any orders.
He wouldn't have to do any ordering.
He wouldn't have to receive anything.
He wouldn't have to sort anything.
He wouldn't have to collate anything.
He wouldn't have to address anything.
He wouldn't have to package anything.
He wouldn't have to send anything.
He wouldn't have to mail anything.
He wouldn't have to do anything.
He uploads a design to a print on demand site, and the generous masses then send in their money. Bret gets a couple of bucks for the tourney, the masses get something tangible.