range finders are usually not accurate at range...regardless of brand type or price...that being said some are better than others. Im not sure about yours. the sun light...dust, fog, etc can distort the laser...not using the laser on a tripod can cause inconsistencies as well. A common culprit is battery life. after a few clicks on a range finder...you pretty much should replace the battery for maximum accuracy of your range finder. GPS or using a mil reticle is probably the most accurate way of ranging something...rangefinders, generally, are quick and easy...and i feel are best to confirm range to the nearest 50-100 yards..
Now within say 300, most range finders id say are pretty spot on.