Old news, with a little scaremongering.
There's been a number of articles spread around, alluding particularly to the US and imports of bogus honey that has been adulterated with various materials - often sourced from Chinese suppliers.
Store bought honey, is just that. They don't usually produce the honey for magical healing properties etc, they process it to attempt to get a particular taste as the blending is done for "eating honey", not fermenting/mead making honey (it's known as "branding", no different from different cola's etc).
If you have a source for local, raw, unprocessed honey, then I believe it usually will make a better mead, but even varietals will have been filtered and heated, even if it's only done to make it easier to package.
Use a reliable source, even if you have to pay shipping (Ha! you probably wouldn't have to pay as much shipping as I do if I want some of the magical sounding varietals advertised for the US market.....)
Somewhere like Beefolks. If you read the "blurb", they quote whether it's raw honey or not....... Raw is usually best as it shouldn't have been meddled with in any way......