Naturally, while in guesthouse, they dined extremely lavishly (8)
I believe the answer is:
innately
'naturally' is the definition.
(thesaurus)
'while in guesthouse they dined extremely lavishly' is the wordplay.
'while in guesthouse they' becomes 'inn' (I can't justify this - if you can you should believe this answer much more).
'dined' becomes 'ate' (I've seen this in another clue).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'lavishly' with its middle taken out is 'ly'.
'inn'+'ate'+'ly'='INNATELY'
Can you help me to learn more?
(Other definitions for innately that I've seen before include "How kids react" , "Naturally, inherently" , "from birth" , "Inherently, instinctively" .)