One rectification: Safe Entry is the same as Fast Track and VIP services (if you use an agent). They are all the same but different agent use different terminology. I speak from experience, you end up in the same privilege line with the diplomat, pregnant women, handicap, children, and so on. But you skip that line as well no matter if an agent sold you a Safe Entry, Fast Track or VIP services. It's all about the same cost, and it's the same section of the airport.
Happened to me late 2024 after 10 years in Thailand so yeah they are cracking down at Nong Khai and every border now. I flew Vientiane to BKK a few days later and got fast track entry with a priority lane officer. Was 6k of tea money paid to agent to get in.
You don't get a denied entry stamp. Officer says you're there too often so they send you to the supervisor room. The supervisor write some stuff on a paper with reason of denial (they can't write "too many entries" so they make something up). He also enter you in the computer system. Then I take the bus to the Laos side again, and I show them the paper and they direct me to a room where they will undo my used Laos visa stamp (as if I never left Laos). So no, I don't pay the Laos visa twice.
I did use an agent, but the agent is never the person waiting for you. The agent is in an office somewhere in Thailand. The agent work with immigration officers. An officer will wait for you near an immigration gate in the airport. They have your picture so they know what you look like. Then you follow the agent through the priority lane to her booth. She's the one who give you the 60 days stamps. So basically the agent work directly with one or more of the immigration officers who stamp your passport at BKK airport.
I would guest that every single officer who work in priority/business line at airport work with one or more agent to make extra money. It's easy extra money for them. And no, you don't need onward travel, that's the biggest myth ever.
I went through a standard priority lane, people there didn't look old nor disabled. I think business class can go through this line. But I skipped the priority lane straight through the booth with officer who greeted me at the entrance. She opened her booth just for me. I just skipped through ahead of people as you do if you are able to miss your flight, for example.