LB: “Maybe they gave fruits?”
I thought of that, but that would have posed even bigger problems when we were in EY. But maybe in the times of the Beis HaMikdash, this issue (of not trusting others kashrus) did not exist to the same extent.
LB: “Maybe they purchased cookies from a local bakery that everyone used at the time?”
That would work. But I don’t know if they always had bakeries. But maybe there were always individuals who ran their own home-baked-goods business as a parnassah.