What I had heard was that anything that isn't "single source" likely has sugar syrup added. this includes all major brands. I wouldn't even trust the expensive "organic" versions of big brands. Apparently exported Chinese "honey" is the main offender which gets mixed with other sources.

Two of the supermarkets in the UK I shop in have their own brand "Spanish Forest Honey", that claims to be single source from Spain. I have no reason to not trust that it is yet. It is about x2-3 more expensive than the big mainstream brands, darker and tastes stronger.

The Spanish producers could be adding sugar syrup as well I suppose, but aside from hunting down honey from farmers markets it's the best option I have.