A good pair of flared trousers has weight to them before you've even stepped into them, a proper drop when you hold the hem and let the fabric fall. Cheap ones feel papery and flap about in your hand like they're already defeated. The ones worth having have a bit of heft, whether it's a dense ponte, a brushed cotton twill, or a wool blend with some give in it, and the flare itself should sit with a bit of structure rather than just hanging there limp.
Mine have had a hard year. A heavyweight cotton pair I bought in the spring have gone through two warm seasons, a lot of sitting on trains, and more than one spin in the washing machine before I learned my lesson and started turning them inside out and washing them cold. The flare held its shape because the fabric had enough body to begin with, the seams at the hem are still flat, and the only real change is that the knees have softened slightly, which if anything makes them sit better. A wool crepe pair I own gets steamed rather than ironed, because a hot iron on a sharp crease in wool crepe will leave a shine you can't take back, and they go to the dry cleaner twice a season rather than live in a washing machine at all. Know which fabric you've bought before you do anything to it, because cotton forgives you and wool does not.
These earn their place from early fiddle around September through to the end of winter, worn long enough that the hem skims the top of a boot and covers it completely, which does more for your leg line than anything structured on top ever will. They're brilliant with a fitted jumper because the volume is all happening below the knee, and they're the trousers I reach for on a day that needs to look pulled together without any real effort going into the top half.
Where they fall short is anywhere you're on your feet moving fast, or somewhere wet underfoot, because a wide hem drags through puddles and picks up mud in a way a straight leg never will. I wouldn't wear them cycling, and I learned that one the hard way, caught in the chain within about four pedals. They also ask for the right shoe, nothing chunky, nothing that competes with the shape, or the whole line gets lost.
The detail that makes the good ones worth the bother is a hem with just enough weight sewn into the lining to keep the flare swinging properly when you walk, not sitting stiff and flat against your leg.