How can it be 'being polite'?!
Do you think 'not able to cum' can hurt working girl's feeling??! I don't think so!!
*Secretly crying in the corner of the room*
Well you may be the prettiest girl in town, but maybe you're just not his type, so he faked cumming to avoid hurting your feelings. I've actually done that before. It's a failed punt, what's the easiest way out with the least drama?