For complex research related real life problems, how can I decide that which meshing will be perfect for the problem and can rely on the final results of that for publication purpose??
The results of any CFD calculation depend on the computational grid quality and size. Therefore, it is important to resolve the grid to an extent that the solution is grid independent. However, grid refinement has a computational cost. Therefore balance needs to be set between desire accuracy and the size of the computational grid.
You need to identify variable which you want to calculate and carried out simulation with different grid size and examine at which grid size your variable becomes independent from grid size.
In addition to the grid independence test, you should compare the results of COMSOL with results of an another published study, i.e. you may need to resolve (using COMSOL) a previously case solved via any other method. The compared with case, may be close as possible as to your geometry. I hope this help you in choosing the right grid size.