BE40 pilot reported on possible exceedance of MGTOW.

Narrative

Last evening; my Second in Command (SIC) reported to my Supervisor at FBO that we took off over the MTOW. Dispatcher X is new to the company and is unfamiliar with The software we use to file flight plans and compute weight and balance. His assumptions are based on numbers that are difficult to determine. And his familiarity with the peculiarities of the fuel tanks is limited.Baggage weight is a guess. Passenger weights are rarely accurate as reported; and are also a guess. None of these items are routinely weighed for accuracy. The fuel gauges are not reliable and never reflect the actual tank capacities stated in the AFM. Variations occur due to the temperature-related; specific fuel density as well; and are not compensated for as they are with the large fuel quantities in heavy aircraft.Even if the caps are removed; it's impossible to determine if the tanks are full or not due to their construction. If the aircraft is not sitting on a perfectly level ramp; the indicated fuel quantities can vary by several hundred pounds. Furthermore; due to lack of biologic (Fuel Additives) treatment on a regular basis; fuel gauges can vary by several hundred pounds due to contamination.The BOW (Basic Operating Weight) is a default number inserted in the FMS. It can be changed by anyone. There is no current 337 in the weight and balance section of the AFM. One must assume that number is recorded elsewhere. And the accuracy of that number is questionable; absent any current 337. Hence; Dispatcher X's computations are guesses. He has no certifiably accurate means of determining the Take-Off Weight at the time of departure.Based on my 2;000 hours of experience in the aircraft; the numbers appeared to be within the nominal limits as best as anyone can determine. While it is entirely possible that several weight and balance limitations have been exceeded during various phases of multiple flights; they are not apparent and not easily determined hard numbers given the vagaries of the measurements involved. At no time have I knowingly or intentionally operated the aircraft outside of published AFM limitations. Any indications to the contrary are well within the margins of error illustrated above. As a further note; FBO aircraft are routinely operated at weights at or near the MTOW of 16;300 pounds. The aircraft performed like it always has with no notable differences in feel or performance.It should be noted that Dispatcher X has failed to meet the performance standards expected of [the] FBO Captain after several months on the job as an SIC.