Air carrier Captain reported a fuel imbalance and had maintenance verify the fuel quantity. The flight was cancelled before the right tank could be verified.

Narrative

Arrived at ZZZ from ZZZ1. The previous crew reported two discrepancies that were documented in the aircraft logbook. First; the travel limiter had faulted in flight; the second was fuel mismatch in flight. After debriefing with maintenance and the replacement crew; maintenance removed the logbook and returned to the Operation's building. During this time; the replacement flight crew prepared the aircraft. The plane was refueled; but no maintenance personnel were observed during or immediately after the process by the replacement flight crew. The fuel receipt indicated XY gallons of fuel were uplifted to the aircraft. (Note: the fueler erroneously entered YY gallons on the receipt). The plane was positioned facing toward the terminal with the Operation's entrance/exit at approximately 11'oclock position from the flight deck. In addition; the rolling stairs used to reach the underside of the plane's wing; needed to observe the fuel indicators; was observed at the 1 o'clock position from the flight deck. When the plane's logbook was returned to the plane at approximately; the logbook contained measurements of the fuel quantity in the aircraft. Applying the procedure; a fuel cross-check was conducted by the crew as follows:Uplift: XY gallonsBlock in fuel: XXXX poundsMaintenance logbook entry: 2;710 pounds left tank; 2;702 pounds right tank= 5;412 pounds(XY x X.X) + XXXX = 4;781.8 pounds of fuel (based upon uplift and block in combined)As a reference; the plane's fuel gauges on the flight deck indicated 2;700 in both the left and right tanks for a total of 5;400 pounds. The fuel gauges operate intermittently albeit; they were MEL'd. A differential of 412 pounds.Maintenance personnel documented in the logbook 2;710 pounds in the left fuel tank; and 2702 pounds in the right fuel tank for a total of 5;412 pounds.The differential of 5;412 and 4;782 was 630 pounds; exceeding allowable error.The Captain requested Maintenance to remeasure the fuel quantity. A new reading of 415 gallons (2;780.5 pounds) for the left wing was obtained. The right-wing fuel quantity was not acquired before the flight was canceled.Summary:Neither the Captain; nor the FO; observed maintenance personnel during or immediately after the fueling process. The fuel quantity discrepancies resulted in the flight crew asking maintenance to remeasure the fuel quantities. The rolling stairs were observed; after this request; being moved to the plane to access the fuel indicators in the left wing.Cause: TBD...suggest reviewing information at ZZZ airport.Suggestions: Recurrent training for fueling.