This suggestion would likely requre quite a bit of coding update - and can't say I've seen any other forum use something like this - but one suggestion that came to mind the other night would be to add drop down selections taht conform to very specific categories one could select when listing their item.
There could be quite a few but probably only 5 or so neccessary for any particular listing:
Manufacturer/General Type (locomotive/car)/road name/specific type (Dash-9/boxcar/caboose/etc)/price.
Above is just a quick swag. There's little doubt the above would need to be refined. Other dropdowns could be added to help narrow the selection down. Some of those drop downs would become very lengthy.
A small comment section for user to add any additional comments.
Not only would this permit listing standardization, but more significantly, this could potentially be used for people to create notifications for something they are looking for. So instead of having to actively browse the WTB forum, or use the correct terminology, an email push could be sent to anyone who is, say, looking for an "MTH" "boxcar" "CSX" "Hi-Cube".
The forum can introduce a push-notification system, vs ea. user having to active pull the information from the forum every visit.
Not trying to turn this place into a marketplace, but there's probably little doubt, lots of business transactions take place via this forum. This may help buyer and seller move items much more quickly and efficiently.
Also would help for folks find that elusive item who may not be able to make it to the forum until later in the day/week, but are able to check emails on a regular basis.