Apple Refurbs are fine. Apple replaces all external parts including the case; only the guts are reused (except for the battery--that is also new).
Do you have a source for this? I'm not trying to be argumentative, but I keep seeing people post this and I have never seen any evidence this is the case. I understand Apple would want to replace a case that was gouged or dinged, but it makes no sense to replace a perfectly fine case on a Mac that was potentially used half a day by somebody before they returned it.