I stumbled on this thread doing a search. I have a focus on hemi carburetors and saw this on ebay. They always have high prices on carbs, but this one struck me as I examined the pictures. You really need to know your hemi carbs to catch this, but this really looks like a restamp carb. What caught my eye was the front idle screw type but also casting differences that are not 69. Looking at the stamping closer the middle 6 and 2 do not look correct, but it sure looks like a professionally done restamp.

So do they just buy and sell this, or do they make the changes?

I will tell you if you're looking for hemi carbs or parts you really need to know your stuff, I am seeing more fraudulent stuff on ebay, and other places and some is by folks you might have trusted as reputable parts dealers.