Earlier quoted context omitted.
I'd say the libertarian's response would be that organizations like UL (which already does work for OSHA) would get hired by the company to certify their workplace, which would then serve as enticement for job candidates. This would essentially make job safety another "perk", like flex time and friday pizza - available to some, based on the scarcity of their skills.
As the “libertarian” (not my label) in question in this thread, the response is that use of violence or violent coercion is morally untenable. Spreading of information so that people can make choices: good Using sticks and guns and shackles to force people to do as you demand: bad Safety can be engineered. Do not bake something unsafe (state enforcement via violence) into the system.
Not to mention that an opposition to state enforcement of minimum wages does not justify the claim that Amazon should reflect the confluence of supply and demand in the market.