What to look for in roses
The outer petals
A real rose does not open evenly. The outermost petals are larger than the rest, looser, often bent back on themselves and a shade paler or browner at the tip. A cheap faux rose has every petal the same size and cupped at the same angle, which is what makes it read as a fabric cone rather than a flower.
The edge of a petal
Look at where the petal ends. A good one has been cut and then rolled or heat-shaped, so the edge waves slightly and sometimes carries a darker rim. A poor one is a clean stamped curve, occasionally with a visible seal line running along it. This is easier to judge in a photograph than realism generally, so it is a fair proxy for the rest.
Garden roses are a different job
An open cabbage or garden rose has dozens of short, ruffled petals packed into a shallow bowl, and one head fills the space three tea roses would. A tight tea rose is a shape rather than a bloom, and works in numbers. Decide which you are buying before you compare prices, because the two are not interchangeable and rarely cost the same.