Hi rkv-

Are " knit lines " a potential weak spot ?

That is a very good question.

My answer would be that I would not purchase a case with a noticeable knit line running vertically along the case wall. Especially it were also observed on the inside of the case clamshell wall as well as the exterior. I would ask the store manager how such a case got through the inspection process with a defect like that.

However your good, and detailed photo does not seem to illustrate that. It appears more as a rub mark, which when you travel and check luggage you may find originating from the from the carousel belt. My wife and I find these all the time on our larger luggage cases, and we later remove them with window cleaner or a degreaser.

Such marks are more easily removed from the Salsa cases that those made from aluminum. But you are heading in the right direction: Always inspect and clean you luggage cases, inside and out, after travelling.