Is the oil an unnatural, pale or golden yellow color? If so, the natural nutrients that give fresh oils their green color may have been refined away.
Does it say it’s from corn, cottonseed, sunflower, soy, palm, sesame seeds, peanuts, rapeseed, or canola. These oils quickly turn rancid once pressed and need to be refined and “deodorized” to disguise the rancid smell.
Also, if it doesn’t say “extra-virgin” or “cold-pressed” on the bottle, then it’s safe to assume the oil was refined.
Oils sold in cheap, clear plastic bottles are industrially processed and no longer need protection from oxygen and light (which naturally cause fresh oils to break down over time).