We saw a family try to do this at a tour of a big state school. The tour guide kindly said ‘Oh, no thank you. That’s not necessary and I’m not allowed to accept that. But thanks so much. ’.
Soon after, we found out it was her solo first tour ever (she was awesome) so then I was even more impressed by how she handled it.
It was a cringy move, very awkward to observe (but honestly, with all good intentions from the tipper, just clueless )