Possibly depending on how well it was set up and how easy it was to use.

To be honest I'd drop the credits thing, it's more likely to get in the way IMO especially with low initial traffic and number of items. I'd just start with allowing members to publish searchable inventory and wanted lists, concentrating on ease of adding and specialised categorisation for models and bits that would allow people to find things with both search and explore scenarios. If it's good enough it could even suggest matches on wanted vs inventory lists and thus those 3 way trades, it just wouldn't try to inject itself in the negotiations.

_________________
Kyrt's Battle Result Tracker (forum post is here)
Kyrt's trade list

Yeah I just think that by imposing a system for the actual payment/value it actually limits what you can do. It is nice for the system to suggest "matches" for trades, but people are quite capable of contacting each other to arrange the specifics. Even if that is a 3 way trade.

Making a list (i.e. a bunch of text) which is searchable is incredibly simple. Allowing faceted search and the ability to navigate items (e.g. finding "fourth edition epic eldar cobra SHTs") is much harder as it requires all the items to be well annotated. If you consider how much of the conversation goes on the trade threads here - "do you have a picture? which edition is it from? is it painted?" it makes sense to encourage items to be well described as then your site can do cool things like notifications of matches. But it is both more complex from a design point of view and can also put obstacles in the way of people listing their items. If you have to assign a game system, scale, material, race, army, painted vs painted for every single item one by one it's going to be limited to people listing odd items, not large lots.

_________________
Kyrt's Battle Result Tracker (forum post is here)
Kyrt's trade list