In dedicating his most-reprinted play, Edward the Black Prince, to the Earl of Halifax, Shirley bespeaks the Earl's protection "as a Briton... as a Merchant... and as a Poet." The uncharacteristically blunt DNB says that Shirley's plays were awful, but Garrick and Drury Lane came back to him, so they must have at least broken even. For our purposes, Shirley is interesting as a self-avowed merchant (his pamphlets are about mercantile issues, evidently) for whom playwriting was one trade--a bit like Defoe perhaps.