Are tuk-tuks ever worth it?

Only for short 5-minute distances as a novelty. They are almost always more expensive and less comfortable than an air-conditioned taxi or a motorcycle taxi via an app.

How do I know if a shop is a scam?

If a driver offers to take you to a 'special gem shop' or 'government-approved tailor,' decline immediately. They receive commissions for taking tourists there.

How to avoid tourist traps and save money in Thailand

Avoid tourist traps by skipping pre-booked 'all-inclusive' island tours and instead hiring local longtail boat drivers directly at the pier. Eat at night markets where locals queue, and stick to public transport like the BTS Skytrain and local buses to avoid predatory taxi and tuk-tuk pricing.

Master the transport pricing. Never ask a tuk-tuk driver 'how much' to go somewhere; they will quote a tourist price. Use the Grab or Bolt apps to see the fair price, or insist the taxi driver turns on the 'meter.' If they refuse, walk away and flag another.
Book excursions independently. Skip the tour desk in your hotel lobby. Go to the local pier or harbor yourself. For example, in Krabi, walk to the ticket booth at Ao Nang beach to buy your boat ticket rather than booking through a third-party agency.
Eat at street-level stalls. Look for stalls with a high turnover of local customers and basic plastic stools. If a restaurant has a menu in five languages with pictures and a tout out front, it is a tourist trap. Expect to pay $2-$4 for a meal here, not $15.
Use public transit hubs. In Bangkok, avoid private river cruises. Use the Chao Phraya Express Boat (the orange flag line) for about 16-30 THB ($0.50-$0.85) to get around the city. It is faster and far cheaper than a private charter.

Are tuk-tuks ever worth it?: Only for short 5-minute distances as a novelty. They are almost always more expensive and less comfortable than an air-conditioned taxi or a motorcycle taxi via an app.
How do I know if a shop is a scam?: If a driver offers to take you to a 'special gem shop' or 'government-approved tailor,' decline immediately. They receive commissions for taking tourists there.