Green’s Dictionary of Slang

1. to flatter, to pander to; thus sugar-mouth talk n., flattery.

c.1600		Shakespeare Hamlet III i: ’Tis too much prov’d, that with devotion’s visage And pious action we do sugar o’er The devil himself.
1931		A. Bontemps God Sends Sun. 51: That ain’t no sugar-mouth talk neither.
1939		R. Chandler Big Sleep 19: It won’t get you anything. Sugaring them never does.

2. to bribe; thus sugaring n., bribery.

1887		Lantern (N.O.) 9 Apr. 5: He hasn’t been sugared by anyone to suppress the truth.
1902		S.E. White Blazed Trail 59: The old-time logger found these two individuals susceptible to the gentle art of ‘sugaring’.

3. to present a fake appearance, to ‘cook the books’, to pose as something one is not.

1892		Stevenson & Osbourne Wrecker 239: Out of six thousand mats [i.e. bags of rice], only twenty were found to have been sugared; ; in each we found the same amount, about twelve pounds of drug.
1894		Daily News 26 Dec. 5/3: ‘Sugaring a house’ [...] in Birmingham..denoting a system of creating a fictitious appearance of business by privately giving away money to be spent at its bars .
1935		(con. 1920s) J.T. Farrell Judgement Day in Studs Lonigan (1936) 552: He wasn’t sure if Loretta really meant what she said and wasn’t sugaring over a catty feeling about Catherine.
1951		S. Lewis World So Wide 37: You might sugar it a little!