Do travelers to Thailand currently need to present a COVID-19 certificate or negative PCR test upon arrival?

They don’t ask for i.i was just there left today the airlines your flying with, needs to see it.

Won't be allowed to board without either a vaccine cert or an official Covid test

Proof of vaccination or negative test results is still an entry requirement for Thailand. Your airline are the ones that are supposed to enforce it when you check-in for your flight.

The health control officers at arrival check randomly. Sometimes 0 people on a flight, sometimes a few people from a flight, sometimes they check everyone on a flight. Random is random.