Unbranded stock can usually be exchanged. Once a garment carries your logo it cannot be resold, so it cannot be returned unless it is faulty. That is why we recommend a size set before a large order.
The line that matters is 'before or after decoration'. Tell us sizes are wrong before anything is stitched and it's a straightforward exchange. Once your logo is on it, it's yours — which is exactly why we push a size set (see below) hard for any order past about fifteen people.
The questions are free. So is the quote.