Was thinking about it. Read through t springs website and here's how it works.

Teespring tldr:

Spring’s fee is included in the base cost of the product. For example, if the ‘base cost’ of a t-shirt is $10 and you set the selling price as $24, you would keep $14 in profit. See product prices here.

They take 10$ per item. Ex 20$ shirt, Beehaw gets 10$ teespring com gets 10$

The amount they take per item varies, depending what type of items

They do a lot of different items. T-shirts, hoodies, stickers