The first thing I do with a strappy heel is check where the straps actually sit against my foot, not just how they look from the front. A strap that crosses right over a bone, or sits too close to the ankle joint, will tell you within ten minutes of wear exactly where it plans to rub. I run a finger under every strap before I even think about the heel height, because a gorgeous shoe that bites across the top of your foot by the time you've walked to the bus stop isn't a gorgeous shoe, it's a mistake you've already paid for.
These don't want to be anywhere near a chunky sock, obviously, but they're also a bit wasted under a long formal gown where nobody will ever see them, which feels like a shame given what you've usually paid for the straps alone. They come into their own with a hem that stops somewhere between the ankle and the knee, in the warmer months when bare legs make sense and the straps get to do their job of making the ankle look narrower. Come fifteen degrees and a bit of drizzle, suede ones in particular turn from elegant to ruined faster than anything else in my collection, the damp just sits in the nap and leaves dark tide marks that never fully lift. Patent and leather cope better with a splash, but any of them do worse with months of being flung into a bag after a night out rather than stuffed with paper and left somewhere flat. Wipe the straps down, let them dry away from a radiator, and they'll keep their shape years longer than the ones that live crushed under a seat. The thin straps are also the first thing to stretch, so a pair that fit snugly in the shop can be noticeably looser by the second summer, which nobody warns you about.
On sizing, go a touch tighter than your usual rather than looser, because strappy styles have nothing structural holding your foot in place, no enclosed toe box doing the work, just you trusting a few millimetres of material not to let go halfway through the evening. Watch the strap across the instep especially, that's the one that either sits flat or digs in depending on whether your foot's a bit higher volume than average, and no half size adjustment fixes a strap in the wrong place to begin with. If there's an ankle strap, check it closes with enough slack for your foot to swell slightly over a long day, because it will.
Would I still love the look of this in an hour, once my feet have actually warmed up in it?