thank you. Based upon what you say, it seems to me that the agent is certainly due a commission because the sale took place under the terms of their retainer to you as agent. I do not think for what you say you do speak this in principle but rather your dispute is as regards ***** ***** of commission that should be due as a result of the above inadequacies in respect of the service.
Analysing this from a legal perspective alone, if one looks at the outcome, you did achieve a sale at the original asking price and therefore there is no financial loss element which you can introduce as a basis for any claim. Accordingly, your basis for any claim for reduction would be based upon breach of contract for failure by the agent to carry out the service they undertook to carry out on your behalf with appropriate skill and care in all respects. He would presumably play and this led to additional work being required on your behalf involving additional telephone calls and also at certain points, potentially endangering the sale will ultimately happily it did conclude successfully.
Accordingly, the holding all payment from the agent may not be entirely wise as I cannot conceive realistically that any decision however favourable to you could conclude that the agent is not entitled to any payment under their invoice whatsoever. Accordingly, as a starting point you may consider making an offer which you consider to be fair and reasonable in all the circumstances as full and final settlement making clear how you have quantified and calculated any deductions you seek to make ( in other words, clearly "show your working"). You can send your correspondence together with a cheque in the amount offered, and if the agent banks your cheque, this is conclusive evidence of acceptance of your offer and it is very difficult for the agent to subsequently claim any further funds from you.
If the offer is rejected, you can advise that you will proceed with a complaint to the ombudsman - I am not aware of any rule in the ombudsman's ADR regulations that requires that you must have paid the agent before you can bring a complaint though the ombudsman may be able to point you to such a rule. In the circumstances, for the above reasons, you may still wish to offer some payment on account to the agent rather than withhold all payment.
if the ombudsman refuses to accept your complaint, as above, I'm not aware of any such provision for them to do so, you still have the right to defend your position in court and it would be for the agent to issue proceedings against you for recovery of any outstanding balance of their invoice in the circumstances and you would have the opportunity to defend their claim. In the same circumstances, it makes sense from your perspective to make any payment you consider to be fair to them either ideally as a full and final settlement as above failing which is a payment on account to reduce the amount in dispute to the actual amount in dispute rather than the whole amount part of which you presumably or failing which would be wise to accept is owed. The benefit of this is that in the event to perceive the course, it would reduce potential costs in court and would hopefully ensure that it is heard as a small claims matter on the smaller sum in dispute rather than a fast track claim for a higher sum which may allow some legal costs to be claimed and generally increase court fees and costs generally