This may be important. Certainly selling T-shirts seems like a way to go.

Successful Amazon Merch account that is doing awesome selling T-shirts? 

I'm trying to make an extra $500 a month and thought this would be a great place to start. I do have a couple t-shirts up but I think I need some more guidance. Is there anybody out there who's selling t-shirts also - I'm super curious to see if you're spending money on promotions, etc.