make a lot of difference in this field, since an experienced detective knows all the secrets and can find even hidden information.
you can ask questions related to experience and also find out the kind of cases the detective has solved previously. someone with experience in your kind of case would be a better fit than someone who has no experience in handling similar cases.
look for a detective who has good links throughout. the job of a detective is to find information, and for this reason they need a huge web of people they can trust.
find out the detective how they plan on finding specific information and see if they seem 