Meat that has been unsupervised

Hi,

One might logically assume that meat was kosher if one knew it had been bought from a kosher supplier.

However: The sages noted that one piece of meat is easily substituted for another without detection, and that there is great profit in substituting non-kosher meat for kosher meat. Therefore, they required that the meat be under protection against substitution from the time it leaves the shochet until the time the consumer uses it.

(Shulchan Aruch Yoreh Deah 63:1; Shach Yoreh Deah 63:5)

Have a great day,
Mordechai