Reckon online price cut has affected tea (8)
I believe the answer is:
evaluate
'reckon' is the definition.
(thesaurus)
'online price cut has affected tea' is the wordplay.
'online' becomes 'e' (as in e-mail or e-commerce).
'price' becomes 'value'.
'cut' means to remove the last letter.
'has' means one lot of letters go next to another.
'affected' indicates anagramming the letters.
'value' with its last letter taken off is 'valu'.
'tea' is an anagram of 'ate'.
'e'+'valu'+'ate'='EVALUATE'
(Other definitions for evaluate that I've seen before include "Reckon worth of" , "Make an assessment of, determine worth" , "'Assess, appraise (8)'" , "Judge the worth of something" , "Make an assessment of, measure" .)