... and "proof of payment," so cannot use "rent a ticket" services. Note they also say return to passport-country ticket, which does not follow official regulations (ticket to anywhere outside Thailand should be OK).
They are making this up, to encourage use of their agent-service partners - at which point, NONE of the requirements are enforced - similar to many extensions in-country.
Although one is unlikely to have all those "requirements" enforced at most crossings, anyone making a border-run without an agent-service should be prepared to stay out 2+ nights, be able to purchase a fully-refundable ticket to their passport-country, and able to purchase a hotel-booking in Thailand, if/when demanded. Also, have the 10K baht worth of cash to show.
"I left my money-cards with my wife/gf," or "in my condo" or whatever won't cut it. Prepare for the worst, and be pleasantly-surprised if things are easy. That is my strategy with EVERY interaction with Thai immigration - even for "no problems reported" things.
"Expected Outcomes" not being met is a source of stress and disappointment, so don't set yourself up to suffer, folks. Always have a "Plan B," and a "Plan C." Don't "expect" fairness, consistency, or compassion - EVER.