I've had many good experiences in private hospitals here but 2 shocking ones:
1) I had a spinal "episode" in 2014 - Bumrungrad told me the MRI showed that the treatment they had given me wasn't working, I had probable spinal cancer and recommended I have exploratory surgery with a quote of about 550,000 baht, including 2 nights in ICU ward, 5 more in genera ward and some dangers associated with the spinal surgery. I said I wanted a 2nd opinion and to her credit the neurologist was happy to recommend someone - turned out she had misread the MRI result, the treatment was indeed working and no surgery was in fact required. Very, very close to spending a fortune on a risky procedure
2) about 3 years ago i had an ear infection and loss of hearing in one ear. The specialist in the ENT dept at Thainakharin Hospital, Bang Na told me the tests they'd carried out showed the damage to the ear was permanent and all I could do was hope for the best. I got a 2nd opinion from one of his colleagues at the same hospital 2 weeks later - turned out the 1st guy got it completely wrong and I only just started treatment in time that saved the hearing. If I hadn't returned for a 2nd opinion and treated the infection correctly I would indeed have lost the hearing.
Moral of story? Always get a 2nd opinion. Even medical specialists habitually make dreadful mistakes here