My first thought is what is your experience as a farrier ?
The fact that you have brought up this questions, even though you may say it isn't you or hasn't happened to you, just wondering what to say, leads me to wonder.
I don't know so will take you at your word .
If you don't feel confident in your ability then it will show and open the door to another person who thinks they might get away with something.
I believe in walking a horse prior to working on it for a number of reasons.
1. If a lameness is present then you should immediately be looking for the cause and making decisions whether to work on this animal or have them call a vet.
2. While the animal is walking I am asking a lot of questions of the owner or person representing the horse. This also helps me make decisions Prior to working on said horse.
3. I am watching the horses deminour so i can be prepared to handle the animal or cautuiously do so should I choose to work on said horse.
All this takes less than 5 to 10 minutes and could or should give you a lot of answers about the animal PRIOR to starting to work on it.
We are not vets, BUT if you have been handling horses and have good experience as a farrier then you should be able to recognise such things in this manner....
1. slide your hand down the leg as you go to pick it up. Let you mind and your fingers feel for any abnormalities/blemishes.
2. Look at the whole horse walking and standing. Does anything standout that draws your attention ?
A cocked ankle.. a slight limp maybe detected by a dropping hip or shoulder or a bobbing of the head during movement...
Swelling in a joint or leg area..
Feeling for signs of ringbone side bone.
And it goes on.. ALL this is an unconcious normal habit that an experienced farrier does without even thinking prior and as he/she begins to work with or on a horse. EXPERIENCE...
Why do I bother to go into this detail ? Because it is habits like this that we use to prevent setting us up for a person reacting with a lawsuit or evwen just bad mouthing us ...
Accidents happen... A hot nail occassionally, a slip of the knife occassionally...quicking a horse can be caused by many things.. a jerking leg,.. pulling away,.. an inexperienced farrier nailing into a thin walled horse,... etc.....
My advice to preventing the senerio you posted about is "Learn the trade and learn or practice something everyday ... No one knows it all... Not even the biggest names in the industry will tell you they know it all. They learn something good or bad all the time...
Knowledge and experience is the best prevenative action anyone can ever take... Its not a cure all but it will give you a more acceptable leg to stand on should a problem arise...
my 2 cents worth