Boy, she's playing with the heart of Peter Sellers (8)
I believe the answer is:
sothebys
'heart of peter sellers' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'boy she's playing with the' is the wordplay.
'playing with' is an anagram indicator.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'boy'+'shes'='boyshes'
'boyshes' with its letters anagrammed with 't' gives 'SOTHEBYS'.
Can you help me to learn more?
(Other definitions for sothebys that I've seen before include "Famous auction house" , "Auctioneers" .)