- Pick up and sell everything.
- Identify all items (including whites with a value of at least 50g) before selling.
- Use collectors for weapons and armor as much as possible - no need for expensive armors/weapons.
- Farm popular common materials and sell in bulk.
- Trade all quest reward trophies for Superior Salvage Kits (not including Trade Contracts - save these for gems.)
- Don't buy skills that can be gained from quest rewards or Hero Skill Trainers.
- Always have plenty of inventory space before a long trip - or carry a mercantile summoning stone.
- Don't buy keys or lockpicks until you're ready for title hunting.
- Know the value of stuff - don't merchant something that may be worth $$.
- Check with the various traders before selling stuff to the merchant.
- Sell unidentified "worthless" golds to players working on their wisdom title.
- Farm Nicholas the Traveller collectibles.
- Sell Gifts of the Traveller rather than hoping for that one-in-a-million result.
- Browse the Guru farming builds section.
- Play through the game doing primary and secondary quests: Don't skip ahead and don't buy runs.
- Don't dabble in trading until you've really learnt the value of things.
- Learn which rewards are worth more than their necessary trophy collectibles.
- Play to your strengths - if you're good at (for example) vanquishing, sell your services.
- If you haven't claimed it already, there's a one-off reward of 50 TRP from High Priest Zhang in the Great Temple of Balthazar.
As a general rule of thumb, don't buy anything you don't need. Just playing through the campaigns makes enough money to ...play through the campaigns!
(There may be further tips to be found in this live thread.)