A key disadvantage to self-report measures is that

A key disadvantage to self-report measures is that social desirability bias can distort findings, compromising the validity of a study. Social desirability bias refers to the phenomenon where participants of a study are dishonest and answer in a way that makes them seem socially desirable. Other disadvantages of self-report methods such as questionnaires include:

1) Wrong answers due to forgetting or poor recall

2) Questionnaires might be misunderstood - leading to low validity of study

3) Low response rates - this is common in questionnaires.