If you play poker, it is the equivalent of pushing 'portions' of your bet out at a time. You push the portion, observe their face and body language, and maybe push the rest.

The 'that was for my assistant' is just something they say to explain away the earlier quoted price. They are pretending that what they said wasn't the quote for this conversation, it was for another, different conversation, between the salesman and their assistant. This only works when the assistant is not in the call.