Excuse me , Ma ' am . I would like to mail this package door to door via airmail to London . It is a very important package and has to be sent within 3 days .   No problem . But , the postage is much higher than the regular package .   That's fine with me . I am willing to pay for it as long as you can guarantee me the package can arrive in time .   OK . All the registered airmail packages can be received in 5 working days .   I see . How much do I need to pay in total for this package ?   It's 500 dollars .   Can I have the receipt ? Just in case I can trace it if something goes wrong . 