A recruiting principle that I always emphasize is differentiation. If you can make your guild stand out in some way, then you have a reason for players to notice your unique waves in an ocean of lookalikes. You may rule out some players who aren't interested in what you're offering, but you will appeal more strongly to the players who like your ideas. It's better to be bold than to be bland.
Your idea is certainly a bold one. However, you can cross the line and create a concept so specific that people just don't get it. That's part of the problem here. Let's break down your guild concept into its components and evaluate them one by one.
Goblins... goblins everywhere
Creating a guild composed of only one race or class is a common theme. It can be fun, especially on an RP server. It gives the guild a more defined and unique identity.
However, it also alienates players who simply do not like a given race. In WoW, race is more than just an aesthetic. Races come with abilities and bonuses that have a direct impact on gameplay and "quality of life."
Changing race also costs real money. So anyone who wanted to join would have to make the choice between paying to race-change an existing character or rerolling. Neither choice may appeal to them.
In and of itself, I think the drawbacks slightly outweigh the benefits here. This is not a huge dealbreaker, but it's holding you back. My advice is to be flexible about race, especially at first. It's better to be goblin "friendly" than goblin "exclusive."
WoW's weak crafting
A guild based on trading is right on theme with goblins. I like it. However, I don't think it's a strong enough pull from a gameplay perspective. The problem isn't so much the idea as it is WoW's crafting.
Unfortunately, WoW has rather simplistic crafting. Nothing you do when you create an item makes it special. Every Chestguard of Nemeses is exactly like every other Chestguard of Nemeses. You can't go out of your way to make your items more awesome except by sticking some gems and enchantments on them, but even then anyone else could do the same (and you don't know what the buyer would want in those slots anyway).
Thus, the appeal of trading as gameplay is far more limited than in other games with more robust crafting. You could try to specialize in items that aren't normally available, such as ultrarare pets and mounts, WoW TCG items, etc., but you need a big investment of gold or real world money up front to pull that off. The Black Market Auction House could be a resource if you have the gold for it, but it will be tough to make a profit on those items, since the minimum bids are always very high.
A trading bazaar powered by an RP addon sounds like fun to me. I'm not very familiar with Gryphonheart Items, so I can't comment on that aspect. However, guild events are a great way to pull in recruits and keep your current members invested.
A guild has to be about more than just a monthly event, however. This idea makes a great supplement to the guild concept, but it's not enough to serve as the core of a guild. You need to offer more.
So what can you do? Let me begin with the caveat that I am by no means an RP expert. But it seems to me that the bazaar could serve as the driving force behind your storylines. What if you create storylines where your guildmates go out on adventures to obtain items (fictional artifacts created by Gryphonheart) to sell at the Bazaar?
That would give everyone the excuse to visit dungeons and raids and even engage in world PvP, and you the excuse to create guild events based on more than trade. Most players want to do at least some of these activities anyway. That would give your players a way to play together throughout the month, with the bazaar serving as the climax of each month's storyline.
At the bazaar, since you probably won't be able to sell RP items for real gold, you could give everyone in your guild a form of RP currency based on their participation in guild play that month. Then players could bid on the items with that currency. Someone in the guild could roleplay a rival trading organization that's trying to outbid your players.
All of this of course will take a lot of work on the part of the officers and volunteer members, but it could be a lot of fun.
Soloing guild creation
Maybe I'm basing too much on the pronoun "I," but when you write "I" instead of "we," it makes me think that you're trying to start this guild entirely on your own. Starting from scratch is a very tough proposition, as I explained earlier this year.
When you start a guild, you need at least a few allies to help you set everything up. Also you don't want your roster to be entirely empty when the first recruits join. It's too late for that now, however.
Set your sights on recruiting a group of players at first, rather than just individuals. You'll have an easier time retaining players down the road once you have a few warm bodies on the roster.
If your guild doesn't work out, you don't have to abandon the idea. Join an existing RP guild that you like. Volunteer to set up a bazaar event every month. If it works well, does it matter whether or not you're the guild leader at the time? What's more important is that everyone has fun.
Officers' Quarters keeps your guild leadership on track to cope with sticky situations such as members turned poachers or the return of an ex-guild leader and looking forward to what guilds need in Mists of Pandaria. Send your own guild-related questions and suggestions to email@example.com.