It depends on your destination, sometimes you don't have a choice of airlines. However, all the cheap carriers are basically the same for the most part. Try using agoda to book your hotels and use grab/bolt for taxi.
From what I've observed in thailand if you don't have money and you have criminal charges filed against you, a lot of jail time is pretty much inevitable.
I actually hate dealing with immigration and have used an agent for the past 3 years... have never stepped into an office since Covid. Some people say its a waste of money and you can do it yourself, but I dont consider the money to be a significant amount considering the time and hassle you save. Time is money.
If you're abusing the system and living in Thailand on tourist visas and visa exemptions, you probably have a very good chance of being asked. If you're a real tourist I'd say the chances are almost zero.