New parts doesn't necessarily mean undamaged parts.

I purchased a Vanagon rear disc brake kit and it was shipped without enough
padding in an overloaded box.  As a result, during shipping the very heavy
box broke open and parts were lost and damaged.  When I finally got things
replaces and was able to install the kit, the calipers seemed a little snug
but I thought they were OK.  Two hundred miles later the grease was running
out of my rear wheel bearings because the grease seals were destroyed from
heat.  A quick inspection identified that the pins that slide into the
carrier were slightly bent and were binding in the caliper.  Evidently,
because the caliper was assembled on the carrier during shipment the pins
were bent when the box was dropped.  Since these pins are not readily
available I had to straighten them and then recut a few thousandths off the
top of the pins so they would be perpendicular where they mate with the
caliper.  Ultimately I got them straight enough to use but they are not
perfect and it took most of a day to correct the problem caused by poor
packing by the seller.

The lesson learned here is you can't assume new means good condition.  There
is a lot of junk out there and sometimes things are damaged in transit.  You
have to inspect new stuff carefully, remembering that it has never been
assembled completely and 100% quality control never happens.

Ed