Just found this addon after i've been looking for one that does exactly this for a very long time, having just moved to a more crowded server.
www.curse.com/addons/wow/lfmonitor

Sadly, it doesn't seem to be functional anymore, does anyone know of an addon that does the same?
Monitors trade for certain keywords and put these messages in a separate window.

LFMonitor

LFMonitor monitors the trade, guild, LFG, custom and general channels for any or all of the following types of 'Looking For' requests from other players:

Looking for Group (LFG)
Looking for More (LFM)
Looking for (LF) a crafter
Looking for Work (LFW)
Want to Buy (WTB)
Want to Sell (WTS)
Guild Recruitment (beta)
Looking for Guild (beta)

Messages are copied to a separate window with an audio prompt. If required, a preconfigured response can be sent to the relevant player from a simple sub-menu.