IANAL; It doesn't appear that OP does any kind of QC, just extra work to say that the labeling on the masks isn't lying. I don't think the liability would be with them unless it was provable that they are lying or are tampering with the masks. They aren't putting their name on a "this won't get you sick" sticker.
On a broader note, if the burden of proof is on the accuser I have no idea how it would be possible to get a lawsuit like that of the ground in the first place. First off, how do you prove it was the mask and not a thousand other things? Also, manufacturers don't say things like "this mask will stop you from getting sick" because they know that would be a really legally stupid thing to say.
On a broader note, if the burden of proof is on the accuser I have no idea how it would be possible to get a lawsuit like that of the ground in the first place. First off, how do you prove it was the mask and not a thousand other things? Also, manufacturers don't say things like "this mask will stop you from getting sick" because they know that would be a really legally stupid thing to say.