They are not "accurate" but good ones can be "precise".
What I mean is, the accuracy is low becauase of how the BF% is calculated. The scales that measure impedance (step on two metal pads, or hold two metal pads) use the measurement and compare to the weight measurement and height and use a look-up table based on data gained from untrained individuals. Large tables using people of various heights and various weights were compiled and the BF% using calipers were input. These table are refered to in your scale. These scales cannot tell the difference between heavy fat people and heavy muscular people. The more "normal" your muscle and fat ratio, the more accurate the BF% reading.
The precision is the ability of the scale to get the same answer repeatedly. Redo the measurement three time in a row each morning for a week. If you consistently get the same answer it is precise.
The best (cheapest and easiest) solution is to buy a caliper set and measure your skin folds (or have someone else measure them. Then use an online calculator to determine your BF% (This is a good one
Body Tracker - Online Body Fat Percentage Calculator ) .
You can then compare the results.
I'm 45 years old and my Tabita scale gives me 32% and a seven-point caliper measurement gives me 23% at 235#.