As someone who is in business, mistakes happen, its a fact.
Its also a fact that even the best companies make mistakes, mainly because we are all human, and its feckin sods law that when a mistake happens its to that customer who needs a smooth transaction more than any other.
Barely a week goes by where I dont forget something or am late for an appointment or run out of a part...sh1t happens, i take a bit of stick from the customer (to be expected really - who am i to trivialise their reasons?!), smile and apologise and move on.