There are lots of farang folks living in Thailand who know a lot about real estate in general. And many who know about construction. Even a few know how to go about getting a house built in Thailand, and a tiny fraction who know how to get "Thai prices" for construction.
Unfortunately, too many of those in each category will be more than happy to rip you off. I honestly believe there is more farang-on-farang fraud than Thai-on-farang fraud in the real estate sector.
If you want to buy on holiday, you stand a very good chance of paying double .. or more. While condos may be a different animal, they represent a different set of dangers, especially when buying off plan.
Most things worth having in life take time to acquire. Friendships, relationships, trust, local knowledge, time, timing and a bit of luck are the tools to get you that dream home.
Houses in Thailand can be very difficult to resell .. especially those bought or built at inflated prices. If you make a bad buy, you are likely to be stuck with it. If you decide that you don't want to live there any longer, you might get a pittance for renting it out. You might simply have to walk away from it.