Accuracy Guarantee: It's more a reflection of their product design, QA systems & labor, and their own testing. I do think they have some more salt when they give out the "test targets" showing it left their hands with a group. While I'm not going to buy solely based on a guarantee it does give the consumer a potential avenue to resolve any issues one may encounter.
One must shoot in the same fashion (bench, bag, bi-pod, vice) as the testing is done with the reasonably same quality ammo the factory used. If you can't hold the weapon, get a good sight picture, etc etc etc...there's no way you will be able to see the accuracy guarantee.
Adding into the factor of ammunition QA there's variables there too. In the end MANY manufacturers are all ready producing quality ammo with their only competition being hand loads. So any "match grade" ammo will suffice to meet the requirements of any accuracy guarantee.
Whether you shoot one brand, one box or 4 brands, 4 boxes it's on you to make a determination as to your satisfaction.
With all that being said IF you make a claim there's a problem and they find nothing......then at least you know where the problem really is.