Is this a fair price?

Someone just quoted you a price. Check it here before you pay — then haggle with confidence (or not, if it's fair).

How to haggle in Bangkok

Only at markets, tuk-tuks and some boats. Malls, 7-Eleven, restaurants, taxis on the meter and massage shops have fixed prices.
Smile and keep it light. Bargaining is a friendly game, not a fight. Losing your temper means you've lost.
Start around half. Then meet somewhere in the middle.
Walk away politely. If the price is right, you'll often be called back.
Remember the maths. ฿20 is about $0.61. Don't spoil a good moment over pocket change.