rekordbox beat grid problems

i have found that some songs that should be very easy for rekordbox to get right are WAY off.I understand that some songs with complicated rhythms may have problems but I have been working on this trying to import my music from serato. most of the songs i am importing have never had anything other than the bpms marked on them. no matter what setting i used it just cant get the grid correct. this really needs to be worked on because this is an important feature!!!!! please help!