Things being what they are nowadays whose to say that "Quality Control" or the lack there off is willing to ship out. I haven't shot a multi pump since I was a kid but I'd have to say that unless the guns were old or at the very least under pressure while en route, I just can't see how a perfectly new O' ring would fail under zero stress. True, shippers can also wreck things rather fast, but their damage is either blatantly apparent or non at all. There is no way for the shippers to mess with the seals and their inherent locations without messing with the rest of the gun.
Now, even on very high end rifles, and I mean the "best of the best" rifles, seals fail all the time after being pressurized by the end user. Would you believe me if I told you that even Lothar Walther barrels are expected to have a percentage of duds? Also, sometimes depending on the application, seals can get damaged during assembly and not be noticed due to the fact once things go together they can't be seen unless tested. More and more companies are willing to play the return game instead of incurring the costs of setting up a quality assurance department. It's all a law of averages, and in this modern world unfortunately, it is the consumer whom has become the beta tester. Roll the dice, for a third time?..