Barcode Markings...

So I recently purchased some comics from the 70's, with a black line drawn through the barcodes on the cover with a marker. I figured marking the barcode like that was done by the person who sold the comics. Whats up with that? How much do you think that would devalue a comic? Say if a comic was in Very fine Condition, aside from a marking on the barcode like that, would it now be considered in just "good" condition. Thanks for your input comic friends...

If a dealer drew a line through my comic's bar-code, I'd borrow his marker and colour his teeth with it after slapping the yellow out. Certain dealers say any kind of marker ink or grease-pencil markings on the cover are verbotten and downgrade a book to VG. The only kind of marking I allow, albeit grumble about, is a neatly placed date stamp. I have an otherwise NM book with a tiny pen scribble on the cover too, I'd toss it out or sell it but it's Amazing Spider-Man #136....

I don't agree with being so harsh about markings on the cover. But I do come at this a little differently since I'm generally a golden age collector so my favorite comics are 60 years old. But as far as I was taught; if the mark doesn't detract from the artwork, bleed through or damage the paper in anyway, it only effects the grading slightly. For a minor mark, it can be considered a crude stamp or store mark and the grade should shift from VF to VF-. If it is more invasive to the artwork or damage to the paper, then drop the grade another point and call it VF-/F+. When the mark is clearly distracting or damaging then the grading can drop to the VG or lower range. Of course, grading is very subjective and I think F- to VF-/F+ is the hardest range to judge accurately.

That said, what would CGC say about a golden age book with a date written with marker on the cover? Assume that the book is otherwise in VF condition and could get an 8.5 without the marking.

I can answer this with an actual grading situation. I have a Black Cat #6 that is physically an 8.0. I had a couple professional graders look at it to help me figure out if it was trimmed or not. They agreed with me and called it a solid 8.0. But there was a neatly hand-written date with curlicues on either side in faded pen above the "Glamorous" on the cover. This put the date dead-center at the top of the page. Pretty conspicuous location in my opinion but the grade came back from CGC as a 7.5 with no restoration.
I think the biggest factor is how distracting the mark is from the cover. If it is the first or second thing you see the grade will be lower than if it takes your brain awhile to click to the date. All things being equal, the date written on the front cover drops a book automatically from NM to VF. After that things like: location, neatness, size, color of ink, color of cover, type of pen, etc. come into play and determine how far down the book slides on the scale.