I'm not sure of all the issues surrounding this, but the below info may be handy as a starting point:
Disputing the bill
If the client considers the bill is unreasonable in the light of any of the above factors, s/he can dispute it. This will involve negotiation with the garage explaining why the client thinks the bill is too high and what s/he is prepared to pay.
While the client is disputing the bill, the garage
can refuse to release the car. This right to keep possession of goods until payment has been made is known as a 'lien'. If the client needs her/his car urgently s/he should only pay 'under protest', otherwise it will be very difficult to reclaim the money later.
At the time of paying, the client should state in writing that s/he is paying under protest. S/he should then send a letter to the garage, repeating that s/he has paid under protest, stating why s/he thinks the bill is too high, and indicating her/his intention to pursue the claim through the county court (sheriff court in Scotland).
Is the garage charging more than was agreed
If the garage gave the client a price before doing the work, but is now asking for more, check whether the price was an estimate or a quotation. A quotation is a promise to do the work at the price agreed. Provided s/he had this in writing, the client can hold the garage to it.
An estimate is only a prediction of the total cost, which may or may not be exceeded. If the final bill exceeds the estimate by more than a reasonable amount, the client can dispute it. The estimate may be used as evidence of what a reasonable charge would be.
Hope this helps... the garage also has a 'duty of care' to your car while it is in it's possession
