The burden is upon you to determine the cause of the failure and prove the
culpability of the party responsible. Since it doesn't appear that you have
determined the cause of the failure, at this point, you are in no position to
assign blame.

john collins wrote:

got a tune up and after 5 min in water splark plug groumd electrode broke
and scored the cyilinder of my 93 18 ft volvo io. Whos liable??