Tried a niche, online T shop with a friend years ago (before Spreadshirt existed). We worked with a local T shop at first but their minimums were a drag. A big T shop in a lower income town about 100 miles from us (we were in Santa Monica) agreed to waive minimums and do drop shipping.

Problem ended up being quality we or the shop couldn't consistently control. It was great for weeks, then bad for a batch, then good again.

Returns and re-shipping costs due to low quality finally killed us.