Analog Sensor output signal accuracy and sensitivity
If you care about accuracy then look for the error specifications in the datasheet. The accuracy is not necessarily correlated with the sensitivity. However, if you really care about accuracy then you will only buy from an established manufacturer that can tell you about how they test their devices and how they calibrate their test equipment.

The "fluctuations" in sensor output will be due to the physical and electrical stuff that you put around the sensor. You won't get that from a data sheet. If you care about long term drift then look for those specifications in the datasheet. If the manufacturer won't tell you and back it up then look for a different manufacturer.

If you insist on buying undocumented equipment from unreputable suppliers then it is your responsibility to characterize and calibrate the sensors. Buy a few extra and do long term life testing so you know what the drift will be.