> There is no customer facing service aspect, and very little quality difference between employees. What quality concerns there are can probably be traced back to an individual employee very easily; returns due to poor packaging or wrong item can easily be pinned on the culprit.

I disagree; a counter argument would be Costco. Almost all of Costco has very little service interaction with their union employees. They have warehouses, distribution, and procurement that has little consumer interaction. It is difficult to find people to point what is what in aisle numbers and the lines in checkout can be very long. As far as I know all of the people who work in these facilities are union and they pay living wages and benefits.

The nice service workers who handle out free samples are contractors, not union employees the last time I checked.