What title you have depends on two factors. The amount of total transactions you made and the ratio between sales and purchases.
A transaction only counts if both parties marked the item as traded in-game.
The titles are:
|Transactions:||33% more sales than purchases:||33% more purchases than sales:||Roughly the same:|
|Under 10||Junior Merchant||Junior Merchant||Junior Merchant|
|25||Experienced Vendor||Experienced Customer||Experienced Auctioneer|
|50||Senior Vendor||Senior Customer||Senior Auctioneer|
|100||Expert Vendor||Expert Customer||Expert Auctioneer|
|200||Master Vendor||Master Customer||Master Auctioneer|
|300||Grandmaster Vendor||Grandmaster Customer||Grandmaster Auctioneer|
|400||Ascended Vendor||Ascended Customer||Ascended Auctioneer|
|500||Legendary Vendor||Legendary Customer||Legendary Auctioneer|
|700||Source of Goods||Not Too Greedy||Jack of all Trades|
|1000||Seller of All||Connoisseur of Goods||The Great Auctioneer|