(no) fun house mirrors
In the past (and a few still do) overclocker's would sand down their chip surface and their heat syncs to remove all flaws ... and on the heat syncs they'd end up with a perfectly flat mirrored finish if they took their time and did it right... and everyone back then was always be amazed, and the overclocker would get better temps with the modified chip and sync.
Now these days most company come out with mirrored surfaces on their products trying to copy what the old school overclockers did in the past but I've almost never seen a Reviewer state the very important fact in their reviews, is the companies mirrored surface perfectly flat. Reviewers always point out, "hey look, it reflexes crap."
An easy way to fully test the sync and add the results to you review would be to hold the sync upside-down and put a drop or two of water on the surface where the sync meets the chip and lay a small piece of glass on top flatting the water out over the surface and you'll easily be able to spot defects if any (using dark liquid food dye instead of water would add to the visibility and maybe possible to photograph).
Most modern glass is flawless, but you'll want to test the glass ... rotate the glass, and also flip the glass while doing the above test to see if its the glass or the syncs surface that is flawed.
Thermal grease is used to remove small flaws involving such hardware, but its always best to have almost no need for grease to get the absolute best heat transfer... you don't want pockets of grease under your heat syncs.
I've bough one of these syncs and it had a lovely mirrored bottom, but it was distorted to the point where the glass seesawed and I had to sand it down to remove the (no) fun house mirror imperfections. I used a piece of square glass, wrapped it in very fine sandpaper to repair the flaw, now the sync & chip sits flawlessly flat to one another.
If I would have bought this sync locally I would have just returned it.