I have sold some t-shirts in this manner, which is one of the primary subclasses of these stores. Doing this has the advantage of access to legit suppliers base

I have sold some t-shirts in this manner, which is one of the primary subclasses of these stores. Doing this has the advantage of access to legit suppliers based in the USA, so you get predictable shipping times and pretty good quality and customer service. However, it's way more expensive, and the quality of DTG (direct-to-garment, essentially inkjet printed t-shirts) is not as good as screen-printing. I now print my own stuff out of my garage and use on-demand printing as a way to validate ideas or fill gaps in inventory.