A hammer has well known metallurgical properties, so anyone can make one. You don't care whom you buy from, but you buy a cheaper, hopefully better made hammer because nobody tries to fleece you for a 100$ hammer.

In the world with only commercial knowledge of hammers, they cost 10G, people spend many years and invest much capital into going to hammer school, and maybe even you just rent a hammer at a 13G a year rate with support. Nevermind the cost for say, a screwdriver.