This, of course, can be considered a
potential weakness or limitation of covert participant
observation.
However, sociologists have successfully solved this problem on
occasions.
Howard Parker's ("A View From The Boys") solution to the "access problem" came through having met members of the gang he wanted to study through a country holiday centre for deprived children. Parker's appearance ("boozy, suitably dressed and ungroomed and knowing the score about theft behaviour and sexual exploits" as he described himself) helped him to gain acceptance by the gang he was studying.