These fraud shops make you deposit first then you go shopping much like how silk rd worked, so at anytime could have seized the coins.

For all we know this screen upon checkout is random, and whoever doesn't complain to get their money back is the cop. Most fraud outfits have major customers they deal with or cashout teams they offer specific BINs over chat, the online store is for bottom tier thieves on public sites.

I don't understand why they tip their hand at all. Why not just sell them randomly generated numbers?

If they really wanted to increase their take they could have that fed identifying system running on the content server as well. That way they can show inflated prices to feds, have the feds try to buy, then walk away with a bigger haul.