A well-designed loadsheet will have in-built protection against usage errors, eg, zone loading, assumed weights, LMCs, completion accuracy, and so forth. Clearly, it is appropriate that crews have sufficient training information to give confidence in this regard.
Unless
(a) the operation requires some further CG constraint and, given that the certification design standards cover reasonable operational requirements, this ought not to be a usual circumstance, or
(b) there is a reasonable suspicion of error - eg an on board W&B system showing an "error" deviation from "normal",
I suggest that a captain would need reasonably strong alternative grounds to reject the loading proposed by ground personnel.
In the world of commercial reality, a capricious rejection probably would create tea and bikkies discussions ...