What are the risks of returning to Thailand on a tourist visa after visiting Vietnam?

You could pay 2000 baht for guaranteed entry, an immigration will wait for you just before immigration and take you straight through ,non questioned asked

Get a visa for the 3rd entry is the best option. By then those immigration officers at the airport will whine at you or deny you entry if you use a waiver.

Last year I was in Thailand on a tourist visa from November to February then I returned to Thailand in April. I went to Vietnam for 10 days in May I returned to Thailand and then in June I went to Japan then I returned to Thailand again. You will not have any problems before you fly in the airport there is a re-entry counter you have to pay 1000 baht and submit one application it takes 3 minutes if your application is ready Mine was ready on the computer, I just changed the dates. I think you should also include a photo. When you return, they will stamp your passport as long as your last stamp was valid. They don't ask any questions my 60 day stamp was expiring in 4 days when I was coming back from Japan they just told me it expires in 4 days I said I know. When I arrived I got another 30 days from the immigration office. The tourist visa is the best visa because you can travel freely and you don't owe them any explanations.

Have things changed so much, I did that in the past. Came over on a tourist visa, then got a re-entry permit after being accepted by the Vietnam embassy. Went Vietnam for 2 weeks, then re-entered Thailand without issue. But was older days, my tourist visa stretched out to 9 months.

Check the Thailand embassy in your home country for Visa options like the 6 month multiple entry visa..

It's a much safer option and you can come and go without worrying about being denied visa exemption entry

You are obviously no tourist. Immigration will notice that. There are reports of people being denied entry with lesser stay then your plan.

If you also plan a trip to Vietnam and re-enter to Thailand I personally would have considered to apply for a six months multiple entries tourist visa at home before I left for Thailand to ensure your stay is covered with a visa. Gives you a 60 days stay with a possible 30 days extension each time you enter Thailand within 180 days.

Condo lease will not help. It just proves your living here on visa exempt or 60 day tr visa and extension which they don't like