Perhaps this expert's a guide to improved relations (3,9)

I believe the answer is:

sex therapist

'guide to improved relations' is the definition.
(relations can mean sex)

'perhaps this expert's a' is the wordplay.
'perhaps' indicates anagramming the letters.
'this'+'experts'+'a'='thisexpertsa'
'thisexpertsa' with letters rearranged gives 'SEX THERAPIST'.

(Another definition for sex therapist that I've seen is " Expert in the treatment of coital problems".)

I've seen this clue in The Guardian.

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