Every beer on this page is labelled gluten-free by the shop selling it. Sometimes that's the brewery's own shop, often it's a bottle shop, and each listing names the shop making the claim.
That label is theirs, not a test of ours. When we checked a sample against the breweries' own websites most of the labels matched, but not every one did. If you have coeliac disease or need to avoid gluten, check the brewery's own information before you buy. Some gluten-free beers are brewed with barley and have the gluten removed, and a few breweries say those aren't suitable for coeliacs.
A beer missing from this list hasn't been ruled out: plenty of shops don't label gluten-free beer at all. Nothing is listed or moved up because a shop paid, and prices come from our last check of each shop's website.