The greedy man was never satisfied with his reward.
Literal
Desire [possessive-の] deep [attributive-の] man [topic-は] that reward [at-には] never was-not-satisfied.
欲の深い is an attributive modifier meaning 'greedy' (literally 'of deep desire'). 決して + negative = 'never.' 満足する ('to be satisfied') takes に for the source of satisfaction. The には stacking adds topical contrast 'as for that reward.'