Fingerprint expert? (3)
This clue is a double definition.
'fingerprint' is the first definition.
(I've seen this before)
'expert' is the second definition.
(Other definitions for dab that I've seen before include "Small North Atlantic flatfish" , "Apply small amounts (usually a liquid) to a surface" , "Bad kind of fish" , "[SOMETHING FISHY]" , "A fish; light touch" .)
(Other definitions for dab hand that I've seen before include "An informal expert such as band had" , "cursory wash?" , "Barely wash" , "Past master" .)