The first thing I do with a strappy heel is pinch where the straps actually meet the sole, because that join is where the whole shoe either holds together or gives up on you halfway through a night out. If it is glued rather than stitched, and you can see the glue line going slightly yellow even on a new pair, that is usually a shoe that will survive one summer and not much more. I also run a thumb over the buckle or the elastic, because a stiff, scratchy buckle that is hard to do up in a dim hallway is a buckle you will fight with every single time you leave the house.
These do not get on with anything heavy on the leg. Thick opaque tights, ankle socks peeking out, a long coat that swamps the ankle strap, all of it fights the whole point of a shoe designed to show skin and show a bit of foot. They are a warm weather shoe through and through, happiest from late spring to early autumn, and they lose their nerve completely the second pavements get wet or icy, because a thin strap gives you nothing to hold on with when a heel meets a damp tile floor. Over months, what gives first is usually the footbed, which goes shiny and a bit grey where your foot sits, and the straps themselves, which stretch out of shape if they are a soft synthetic rather than a proper leather. I keep mine out of direct sun when they are not being worn, because cheap dyed straps fade unevenly, and I wipe them down with a damp cloth after any night where they have touched grass or a sticky floor, which, if you go out in Liverpool, is most nights. On fit, the main thing to watch is where the strap sits across your foot, because if it crosses right over a joint or a bunion it will dig in within the hour no matter how good the shoe looks standing still in the shop. Go up half a size if the straps feel snug when you first try them, since they rarely stretch much, and always walk a proper lap, not three steps, because the first wobble on a hard floor tells you everything about whether that heel height actually works for you.
Before I hand over my card, I ask myself one thing: can I still walk normally in these after ten minutes, or am I already doing the careful little shuffle that gives away a bad buy by the end of the night?