I will not buy a sandal I haven't walked across a shop floor in, twice, because the first thirty seconds always lie to you.
The difference between a sandal that lasts the summer and one that's bin bound by August is almost never visible in a photo. It's in the footbed, whether it's a proper moulded shape or just a flat bit of foam pretending. It's in the straps, whether they're backed with something soft where they cross your skin, or just raw leather that looks fine until hour four at a barbecue when it's cut a line across the top of your foot. It's in how the sole is attached, stitched and glued rather than glued alone, because glue only sandals start separating at the toe within a few wears, usually right as you're stepping off a kerb. Buckles and sliders matter too, cheap metal goes dull and sometimes green against damp skin, and a strap that won't hold its hole stretches out within a month and leaves you walking out of your own shoe.
A good pair earns its stretch marks gracefully. Leather softens and takes the shape of your foot, which is exactly what you want, while a poor synthetic just goes slack and never looks right again. Expect the footbed to darken a bit where your foot sits, that's normal wear, not damage. What kills sandals faster than anything is leaving them in a damp bag after a day at the beach or a festival, so wipe sand and sweat off before they go back in the cupboard, and let them dry properly rather than shoving them straight into a wardrobe. A bit of leather conditioner every few weeks through the season keeps straps from cracking, and rotating two pairs rather than living in one stops any single sandal from collapsing under constant use.
Flat ones and sliders are your everyday, dog walk, school run, errands sort of sandal. Something with a heel or a wedge earns its place for anything with a bit of occasion to it, a lunch, a wedding in a marquee, a day where you want your legs to look longer. Flip flops are strictly poolside and garden, never pavement for long. Pair simple ones with a plain dress and let the shoe do nothing clever, or put something with a bit of height under wide leg trousers so the hem skims the top rather than dragging underneath.
Tomorrow morning I'd put flat tan sandals with a linen shirt dress and not think about it again until I'm taking them off at the door.