erchin 6a - nidvas Akum

As we asked in shiur -- if the goy is actually bringing the present right away then what רפיון ידיים is there?
This seems to be the peshat of the Rabbeinu Gershom who says that הא בתחילה is that we tell the goy, no thank you, but if he already brings it (even though it is בתחילה) we accept his nedava.