Bob,
I don't know the seller of the Flip site and I could see where it could be possible to not notice the enlarged hole. Maybe overlooked by both the Seller and those bidders.
But for that price tag, lessons learned.
As far as the D tip sling seller ...... Way back on one of his early sales, a positive feedback was left but the buyer stated that these were considered post WWII.
So he was told years ago.
I have all the C tips I need, but when using a sling I use a D tip. No reason to put the wear and tear on a pricey C tab when a D will do the job.
Side note: Nascar runs at Michigan this weekend.