I had a slightly similar experience posting three parcels off to the nieces end of last week. I was cross-questioned:
"What's in them?"
"Why do you want to know - they're not valuable ...."
"We have to ask"
"Well, how should I know? Mrs O made up the parcels, I'm just the courier ..."
"Well do you have any idea?"
"Well, that flat one, must be a book"
"That's OK then"
"The others ..... <racks brain> That one's a Lego set!"
"That's OK then - what about the third parcel"
<looks sly> That must be Lego as well"
"OK, then, that'll be £8.45 ........ have a leaflet for future reference"
Lady next to me was having a similar problem, posting parcels for someone else .....
Went home and gave Mrs O the leaflet.
"What did you say was in them?"
<Triumphantly> "I said Lego sets!"
"That was last year ......."