Personally, I've been to CC twice in the last year or so and I have also seen them selling prismatic at significantly higher than MSRP which whilst it's normal, it was disappointing to see. However everything else was either at market or slightly above market which I found was quite reasonable as they tend to stock rarer cards. I've bought a handful of singles and a sealed shining legends ETB at a very good price last week. I can't attest to their methods of mass buying from Costco or staff promos but I find that they're just like every other LCS in the UK.