The give away is the sole, not the strap. A platform sandal that's going to be any good announces itself after about three weeks, when the wedge hasn't started crumbling at the edges and the footbed hasn't gone shiny and hard where your heel lands. Most of them look identical in the shop. It's only once you've walked a few miles in each pair that you find out which one was built to last and which one was built to be photographed standing still.
Stick to the plain shades if you want one pair that works for everything, a tan or a natural raffia colour that doesn't shout, or a black that you can wear with bare legs without it looking like you're trying too hard. The white ones are lovely for about a fortnight and then start looking tired around the toe, scuffed in a way that doesn't polish out. If you've got none and you're starting from scratch, go for a mid height platform rather than the tallest one on the rail, something with maybe an inch and a half of lift, because you'll actually wear it on the days you'd otherwise reach for trainers, and a sandal that stays in the cupboard isn't doing anyone any favours.
They sit well with the clothes you already own rather than anything new you need to buy for them. A straight linen trouser, a simple cotton dress, denim shorts that have gone soft with age, all of it looks more finished with a platform under it than with a flat sandal, because the little bit of height does something to how a hemline falls. Before you pay, check the strap where it meets the sole, that's where cheaper pairs let go first, and have a proper look at the stitching round the footbed rather than trusting the way it looks sat on a shelf. Press your thumb into the platform itself. If it dents and stays dented, it'll be collapsing by August.
The ones that last through a season of being kicked under a café table, shoved in a bag after a wet walk, worn with no socks on a hot pavement, tend to be the ones with a slightly thicker rubber platform rather than cork, which looks nicer on day one and sadder by week six. Cork can be lovely, I'm not ruling it out, just go in knowing it marks.
Tomorrow morning I'd put mine on with a loose linen shirt dress and nothing else decided yet, which is rather the point of a good platform sandal.