Nancy Drake,
Interesting about the story where you were invited because somebody had an ulterior motive. In this case it was about fishing for information. I know I have been invited as the entertainment because of a story I can tell. In this case they talk endlessly after you leave.
My observation was that some invitations were a 'hook' to try to get you to do favors. They reasoned that because you were served a meal you would then be more receptive to such things. Other invitations worth refusing were those for 'sales parties' for the many products that JWs sell.
When I discern that invitations are not about somebody sincerely trying to befriend me but are instead about selling something or getting favors then I consider these to be ulterior motives.
LHG