@bluedolphin-- No, there is no way to cheat a saliva THC test. Regardless of what people may try, since the test is done under observation and is supervised by someone the whole time, it's not possible to cheat.
Since THC in saliva can be measured for only up to 72 hours after smoking marijuana, it's best for post-accident testing, to see if an employee was under the influence while working. Urine testing is better for general THC testing, to find out if an employee is a regular user of the drug.
But you can be confident that the saliva THC test results are accurate When a drug enters the bloodstream, it ends up in saliva very soon after that. So you can be sure about whether an employee's work was effected due to marijuana use.