All they need is a checklist and/or a few intelligent people to check their proposals.

1 Covid infection rates in "preferred" countries for visitors.
2 Rules for people leaving the other country
3 Rules for when people return to the other country

Then add checks against every single rule Thailand intends to impose.

e.g. For point 3, if they think they are going to allow loads of Chinese tourists in, they also need to remember China has 2 weeks of "proper" quarantine when people return home. No quarantine at home -it's confined to a hotel. So very few tourists will come from there.

If Thailand sets up realistic quarantine rules for some European countries, they might get a few visitors.
Make the quarantine options as pleasant as possible, combine with a no-hassle 120 day visa waiver & don't add any additional dumb restrictions. That way, they might just get a few people going to Thailand for the winter (mainly retired & financially independent people).