Can you really tell a good fake plant from across the room? Mostly, yes, within a few seconds, and it almost always comes down to the leaves catching light the wrong way or the pot looking like an afterthought. The plant itself fools people for a moment. The container usually gives it away first.
The ones worth having hold up for years without much fuss, which is the whole point of buying fake in the first place. Dust is really the only enemy, and it shows up faster than you'd expect on broad leaves like a fiddle leaf fig or a rubber plant, so I wipe mine down with a damp cloth every few weeks rather than letting it build into a gray film. Faux stems made of a firmer plastic keep their shape through seasons of sitting near a sunny window, while the cheaper, floppier kind can start to sag and look tired after a year, especially if anything heavy rests against the leaves. Vases fare better with almost no care at all, though ceramic and ceramic look alike enough on a screen that I've been surprised twice by how light a piece felt the moment I picked it up.
When something arrives, check the base of the plant first. A good one is weighted or set in real foam and soil mix inside the pot, not just jammed into a plastic sleeve that tips over the second a window is opened. Fan the leaves out by hand, since they get flattened in shipping boxes and some materials hold a crease if you leave them folded too long. For vases, run a finger along the rim and the inside seam, because that's where you find the rough patches or a slightly off centered mold that a photo will never show you.
Where these go wrong is mixing finishes that don't belong near each other, a very glossy, obviously plastic leaf next to a rough linen sofa reads cheap in a way that a matte, more textured leaf simply doesn't. They also don't love damp bathrooms over time, the trapped moisture can warp a cheaper pot base even though the plant itself won't care. And skip them entirely in a kitchen that gets real grease in the air, since that film is much harder to clean off silk leaves than it is off a real plant you can just rinse.
The detail I actually love is finding an arrangement where someone bothered to vary the leaf sizes within one stem, young small leaves near the top, older bigger ones lower down, the way a real plant actually grows.