We often get criticised fo the amount of advisorys we put on the invoice, but the times it has saved us from customers making false claims is well worth the hassle of typing them up and being accused of 'plugging for work' We can't be responsible for vehicle owners ignoring the advice and guidance they pay us for, can you sue a doctor because you ignored his/her advice not to smoke ? ( Ok, maybe in America ! ).
We have a duty to discharge our knowledge of the vehicle's condition to the customer, and on the invoice is the best way. If a customer pays the bill, it is seen as their acceptance of what is on there ( which includes the price ) unless they sign it saying 'paid under duress' or something like that as I recall.
We once had a wheel come off a vehicle, not a thing you would like to post on a public forum I know, but it's a good example for garages and customers alike, so I'll risk being shot down.
We fitted the spare wheel to this vehicle, and the wheel ( and the wheel nut holes ) had a fair amount of surface corrosion, although not bad enough to be overly concerned at the time. We advised this on the invoice, also stating that it should be renewed. A week or so later we got a call, the wheel had come off on the motorway, no one hurt thankfully & only minor damage to the vehicle. When we looked at it ( with the customer there ) it was obvious that the metal on the taper seats had crumbled under the pressure of the wheel nuts and the weight of the vehicle & the nuts had therefore lost their bite & loosened. The corrosion had gone deeper than we could see & had undermined the taper seats. I must stress that It DID look servicable at the time, this was totally unexpected, freaky even.
Because this job was so recent I recalled the advisory & took a copy of the invoice out to the scene, along with my heart in my mouth. Customer was fine, they bought a new wheel & it was put behind us. They are still a customer too, and now always read the little 'plugging for work' notes on the bill !!.
Now, how many of you would make an advisory about a spare wheel being corroded during a service ? Glad we did !