Question about the online market

So if you look on Ebay you can find a 1940's Mercury dime graded in MS 66 for $35 or so. Which is great for the buyer, but that's a $35 coin in a $25 slab. That said, it would have to be really good deal for me to consider buying an ungraded coin sold as MS 66 because I just don't trust Ebay enough so I understand why sellers would get coins slabbed, but I would think they would at least charge a premium for it, no? Has history taught sellers that buyers won't pay more than the coin is worth, slabbed or not?

Are these sellers getting coins raw and hoping they hit the jackpot on a MS68 FB and just counting their losses or what? They can't be making any money off of the $35.