I ordered a shirt from here (after checking my own size requirements, mind) and found it to be a bit too small (the world really needs Medium+/Large- options). After emailing them asking if I could return it for a replacement/get a discount for one, they just shipped me a Large for no additional cost or even asking that I send it back! Repeat customer right here.
They also have a size chart lot and of options for material (go for Ringspun, the extra comfort is definitely worth it) and the prices are competitive.
[Pic is what I bought]