You are bidding on an E-Booklet. This is very imformative with wiring diagrams and explanation that anyone can understand. Many times when a 3-way switch is replaced the wires are not connected properly and the switch will work on one side and not the other. With several different diagrams, this should cover most situations.
I propose that he has one of the splices wrong. It is the one that he has the feed at the light and dead-ended the (2) 3-ways. In his splice, he will be using one of the whites as the return to the light thus having (1)white as neutral and (1)white as switch leg. Anybody agree?