There is no standard tolerance level established per trait. Markets vary on required tolerance levels. Pollen drift is uncontrollable. Problems with traits can occur after the growing season. Accuracy of the test is dependent on the sampling procedure and the sample size.
Present testing is limited to very small sample sizes.
Growers can take the following steps to improve their position. Keep receipts to prove what seed was planted. Know what the neighbors planted to determine isolation plans. Create grain with less GMO's by using isolation techniques. Plan the final use of grain before planting.