Possible Clues:

• Hack's novel
• This be poor Lit badly written
• Book written to make money on grass heating unit
• Elevated work? Hard worker's penning book — one of lesser quality
• Be pro, toil frantically to produce this lucrative work
• Work of literature produced just to make money
• Work of pulp fiction
• Provides the heat after drugs found in library
• Post Office worker pockets black book that's an earner
• Probe toil that's awful work done out of economic necessity