French Indo China 1908 A - Underweight

Thanks to all for the excellent advice. I'm a little hesitant about a slide, only because of the fear of small scratches inflicted on the coin as a result. I have some very nice coins that would have graded PR70 if somewhat hadn't tried the mistake of cleaning them with a rough cloth. Small scratches are readily apparent under 7x. So, they get downgraded as a result, simply because there's no fix for that. Also, the NGC grading phrase that catches my eye most is that starting at MS60, there can be "no discernable wear". I have some ANAC Morgan coins that are boldly graded MS63 and simply are not. With Morgans, the problem area is always the breast of the bird, or high points on the wing edges or in the hairline. Some coins, such as German or Mexican coinage, I look at the details of claws, or the minute detailing in the crest. In this case, the bird's breast was worn smooth, no cross-hatch of feathers at all. The rest of the coin was great, except for that. When it comes to grading, I find the only solution is to be absolutely brutally honest. Otherwise, over time you come to think you have some awesome stuff which you do not.

I used to think the same thing earlier when I began accumulating fake coins for study and documentation.
In this case the seller has a reasonable question.
Might not make sense as the seller presumes.
But I learned the seller just has mistaken belief.
Certainly a magnet slide would be improper for a highly graded coin.
A slide would have no value over a suspended coin or suspended magnets for an initial silver check.
I use my slides for show & tell with customers weeding out good and bad coins that are presumed to be silver.
No coins in any population are candidates at all for potential grading.