Fully aware of this stipulation. I am however suggesting this with relevance to trying to avoid a positive when you get to Thailand. If you can self isolate 5days before the initial PCR test then the result of that initial PCR test is pretty much a true negative and indeed you are negative. Then just continue to self isolate between the initial PCR test and the flight and you should be home free. Anything that happens at the airport, airplane, airport, taxi to hotel, will not show up on the PCR test in Thailand.
Just a suggestion if you are worrying and if indeed you are able to follow this plan.