Originally Posted by $5 submissions

It depends on WHEN you placed the cart there. If the person backing out did not have a CHANCE to see the cart since you placed it IMMEDIATELY before they backed out, then you are probably negligent. If you left the cart there for a long time and they STILL backed out on to it even though they had AMPLE OPPORTUNITY to know of the risk, then it's their fault. However, since you were both negligent, in the latter case it might be a case of contributory negligence and you might pay a % of damages.

Disclaimer: This is not meant as legal advise. Consult a local attorney.