Not sure about now
........but it's all about Location,Location,Location.
When I lived in Koh Samui I built a House and brought a 2 Rai plot of land as well ( 15 Years Ago )
The 2 Rai plot I brought for 600,000 was resold a few years later for 1,200,000 ( minus tax )
I also brought a 1 Rai plot for 600,000 with a friend and we divided it into 3 plot ,he built a house ,I built a house and we later sold the 3rd plot for 450,000, so mine and my friends plot which we built our house's on only cost 75,000 each
On my Plot I Built a House with a Swimming Pool for 2,000,000 ( including the land price ) and sold it for 3,500,000 . I did here the guy that brought it later sold it for 6,000,000 +, and I hate to think what price the 2 Rai plot of land I sold is worth now ???... In Hindsight it could have been a nice little nest egg if I had not sold them , but it's too late now to start thinking about 'If's' and 'But's'
And I was quiet happy with my returns at the time .
I had a Company and did everything above-board
Not sure if it could still be done today though, but I'm quiet happy living in our House here in Surin that was build from the profit I made on just the Samui House sale
BTW..No way would I trust a Company like the one in the OP !!!