immigration has all your entry, and exit details. They also don't start processing your application immediately when you apply. If your immigration exit stamp shows you left Vietnam before they started processing your application when it came up in the queue, you better return immediately and send them proof you are there, or the rejection can be expensive. They asked for proof you are in Vietnam. What happened to others has absolutely no relation to your case at all. You can't argue with them. If you don't return, and your immigration entry stamp shows it, no matter what you say, they will reject you. They do verify your location by your entry, and exit notations in the computer. They know exactly when, and where, you entered, and exited the country, as it is all in the immigration computer system, and for every country you've entered and exited.
As it stands now immigration hasn't set the rules to maintain the soft power visas. They will set rules as more people try to scam the system, as you are suggesting. With any other visa if you don't meet, and maintain, the requirements of the visa it is cancelled. There will be rules covering this with the DTV visa, they simply haven't been drawn up yet, but they will. Thailand always believes people will be honest, until they prove them wrong, at which point Thailand corrects, and puts rules in place to prevent the scams
you are not giving true advise. Basically you do not know what you are talking about, and operating on hearsay, which is decades old, and no longer true.
this is the easiest way. Make an appointment at the Thai consulate in savannakhet Laos first thing. Then you should already have the rest of the documents on this list, under visa type on the website. You'll get your 90 day type O entry visa, then extend it in Thailand for the year after your money is seasoned again for at least two months. You started over just like before. It works best if your wife is with you, but not required for this part.
The proposed ETA has been incorporated into the bt300 entry fee, that includes basic travel insurance, that will go into effect sometime in the months to come, first on those flying in.
As long as the gym you are training at is legally licensed, and provides you with a letter stating you are taking regular classes with then, together with your bank statement showing your bt500,000+ balance for the last 6 months, to cover the requirements of any country surrounding Thailand you go to to apply for the DTV visa. They all don't want 6 months of bank balance, but a few do. Those things are all you need, together with your passport of course.