I probably should know this but ... what are the rights of the representative of the estate to appeal an overpayment decision made against a deceased's estate which is being recovered from the representative (there was an estate but client spent it -the overpayment actually relates to overpaid benefit during the deceased claimant's life)?

I think the representative has the same rights of a appeal as a claimant would. I know I've lodged an appeal in exactly the same situation and had no problem.