Buying a used lens with a scratch - how to troubleshoot

[Faultlinespine]

I’m close to pulling the trigger on purchasing a used Sony 24-70mm gm lens. It’s about $300 cheaper than others and the only flaw is a small scratch on the very outer edge of the lens (as seen in photo). 
I’m new to the camera world and wondering if there’s a test or method to check if the scratch will impact video quality. Even if there’s a small reduction in quality, I wouldn’t go with the purchase. My untrained eye can’t tell if the contrast or clarity of the image is impacted by looking through the monitor. Any thoughts appreciated.

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[FunWithCameras]

A scratch on the front element will not be visible in the images. It will be out of focus and blurred out of existence.

There is a slight risk of introducing a flare, and there is a standard way to fix that which will sound silly. You fill the scratch with black ink! I don't know if it still exists, but the recommendation used to be to use "india ink". You want the ink to fill the scratch, but not overflow, so a thin ink is better. If you don't want to try the ink, then shooting as-is should be fine.

Not sure that $300 is enough discount, though, because reselling the lens with the scratch will be more difficult. I'd be inclined to push for a bit more of a discount...

[XKAES]

I agree.  That's nothing.  Take a black SHARPIE and dab it -- to avoid possible bright spot.  If $300 is a 25% discount (or more), I'd go for it.  With the savings, buy a multi-coated UV filter to avoid more scratches.

Edited October 16, 2023 by XKAES

[Faultlinespine]

Thank you for the advice. If there’s only a remote risk of lens flare (and I can fix that with ink) then it might be worth the $700 US they’re asking. At resale, I would mark the price down similarly.

[Phormula]

Yes, the risk is very remoted and only in specific lighting conditions.

A few years ago I took some pictures with a cracked polarizing filter. I did not realise immediately because the filter cracked by itself from side to side, without being smashed against something. When I realised, I took the filter out and I shot the same pictures without the filter. When I looked at the pictures, I saw no difference except in the one that was shot with the sun directly into the picture.

[Monochrome]

See Roger Cicala of Lensrentals who has dealt with 1000's of lenses post on Front Element Scratches. I think the lens you are considering will be just fine as far as that scratch goes providing it did not result in mis-alignment of the front element.

He also has a practical guide How to Test a Lens.