It is possible that they get them from a liquidation sale where goods are sold for pennies on the dollar. Alternatively, the items may be refurbished or reconditioned items.
There you go, Quantity of 10 gets you bulk pricing after the discount. . . . can you use 10 breakers right away? If not, pay retail for what you need and bank the rest…
I do recall Amazon offers some electronics in bulk that you can buy in singles. I bought a micro SD card USB adaptor for .35 cents not too long ago from there.