A long-standing problem of liquid-marble based technology is the inconsistency of the effective surface tension values. This inconsistency could be due to particle size, particle type, volume of the liquid marble or the preparation method. The prevailing liquid marble preparation method is to roll a droplet on a powder bed. The lack of control of rolling duration or revolution speed could contribute to the inconsistent effective surface tension values. We hypothesize that a systematic preparation approach could improve the consistency of the effective surface tension values. In this work, we (i) determine the effective surface tension using the natural oscillation of a sessile liquid marble and (ii) investigate the effects of liquid marble preparation methods on the effective surface tension for the first time. We find that the effective surface tension values of a liquid marble prepared manually are inconsistent. In comparison, a systematic preparation method improves the consistency of the measured effective surface tension values. Interestingly, the systematic preparation at higher revolution speed causes interfacial jamming at the liquid marble shell which decreases the consistency. The results from this work can provide a deeper understanding of the fundamental characteristics of liquid marbles.