The first thing I do with a wide fit sandal is pinch the strap across the widest part of my foot and see how much give it actually has, because half of them are just a regular sandal with a slightly longer size run and a sticker that says wide. A proper wide fit widens at the forefoot specifically, where the bones splay when you walk, not just end to end like someone stretched the whole shoe on a rack.
Where this goes wrong is if your width problem is actually a height problem, a high instep rather than a broad foot, because then a wide sandal gives you room in the wrong place and your foot still slides forward with every step. It is also the wrong choice for anything with a delicate single strap across the toes, since wide feet tend to need the strap higher up, closer to where the foot actually flares, or it just cuts in no matter how roomy the rest of the shoe is. And if you're prone to swelling by the afternoon, a sandal that fits perfectly at ten in the morning in the shop is not a reliable test.
In the shop, I check three things before anything else: whether the footbed has any texture or grip, because a smooth one with a wide loose fit means your foot slides sideways on it all day, which defeats the point. I check the buckle or adjuster sits somewhere you can actually reach without contorting your arm. And I run a thumb along the inside edge of every strap, because the cheap version finishes that edge with a seam that's fine in the shop and turns into a blister by the second wearing. A good one binds the edge properly or uses a soft enough material that it doesn't need to.
They clash with anything narrow and architectural above the ankle, skinny cropped trousers with a tapered hem especially, because a wide, flat sandal under a narrow leg line just reads as two unrelated decisions made separately. I'd also think twice pairing them with very delicate, fussy dresses, the sort with tiny details at the hem, since a chunkier wide fit sole tends to want something equally straightforward on top.
Buy them a touch big rather than tight across the widest part, since width that's slightly loose softens over a day and width that's slightly tight never does.