There are many times in which I forgot to  pay bills after buying something and then went away with confidence. After a while ,I remembered it and then went back to pay money with doubt that why I didnt pay money and to my surprise, no one stopped me to go . So I think the key is that I look like a honest person ,no one think I dont pay money , but I can not use other 's trust to me to do some bad behavior ,so I must go back to pay money and apologize. after I go away , I hope they say that how good I am.