They can file a report at the police. The police will know where he is when he does 90 reporting, gets a new visa, wants to leave the country. It isn't rocket science.
If he had a friend he wouldn't have to ask here.
He is asking here in the expat community.
That you can't trust a Thai is racist, there are like with any nationality good and bad people.
Not going to work for several reasons: 8 manual dishwashers are quicker than your 6 machines, you need people to feed the machines, unload them and store the washed items.
There is a penalty if you sell the property within a certain amount of years, can't remember how many years.
Property Taxes in Thailand | Siam Legal International (siam-legal.com)
More recent:
Thailand Land - Taxes on Selling | CBRE