https://github.com/EQEmu/Server/blob...ding.cpp#L1750
https://github.com/EQEmu/Server/blob...cket.cpp#L1094
Those will get you into the neighborhood of the buyers message.
https://github.com/EQEmu/Server/blob...cket.cpp#L3657
https://github.com/EQEmu/Server/blob...ding.cpp#L1754
Same for bazaar search...
I definitely can't guarantee that anything you change in those functions will help you along the way..but, that is where both activities are handled.
You might try turning on 'gmsay' log output and watching any related messages.
When I work on a system, I usually do that so that I can monitor actual packet flow associated with any activity.