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 |
10 | Vendor | Customer | Auctioneer |
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 |